What to use
Celebi @ Life Orb / Leftovers
Trait: Natural Cure
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature (+SAtk, -Atk)
- Nasty Plot
- Giga Drain
- Psychic / Hidden Power [Ice]
- Hidden Power [Fire] / Earth Power
Role: Special Sweeper
What It Does: Now that Tornadus-T got banned, this set is even better than before. Now that Tornadus-T is banned, and not all Rain teams are going to use Tornadus, this set is a terror to rain teams, although it can also be good against other types of teams, such as Sun (when the sun is not shining, of course). This set takes advantage of the fact that the most common set to Celebi is Specially Defensive. Thus, many times, it can force Sheer Force (pun not inteded) Landorus, and Keldeo, out, and take advantage of this to setup a NP boost. Although Celebi is not that speedy, it has many advantages over other sweepers like RP Landorus. The first is that it has many good resistances to Fighting, Water, Ground, and Electric. The second is that Celebi is not weak to Stealth Rock. Also, should Celebi be statused, it can simply switch out to cure itself. Also, Celebi is weak to Ice Shard, although Mamoswine can never OHKO Celebi at full health, and will be OHKOed by Giga Drain in return. Celebi can also take Bullet Punch incredibly well, and resist Mach Punch and Aqua Jet althogether.
Nasty Plot boosts Celebi's Special Attack to incredible levels. The main sweeping move is Giga Drain. Although Grass isn't the best STAB to use offensively, as it is resisted by many types, it also hits Water- and Ground-types super-effectively. Plus, Giga Drain can heal Celebi, mitigating the Life Orb recoil.
The third slot goes to a move that Celebi will use against Dragon-types. Psychic is the recommended one, as it also receives STAB, and will have good neutral coverage against things that resist Giga Drain. Also, Psychic hits Fighting- and Poison-types super-effectively, and this is very important against teams that need a powerful weapon against Fighting-types. After a boost, Psychic is also able to OHKO most Dragon-types. Hidden Power Ice can be used instead. This is because Psychic needs a boost to be able to OHKO Dragon-types reliably, and Hidden Power Ice can do this without a boost. Also, Hidden Power Ice hits three Dragon-types that resist Psychic: Lati@s and Hydreigon. It also hits Landorus without having to resort to Psychic, as Sheer Force Landorus cannot OHKO this Celebi, but has a chance to 2HKO with Hidden Power Ice, but Celebi can't OHKO in return without Hidden Power Ice. Finally, Hidden Power Ice has a high chance, when boosted, to OHKO 4 / 0 Dragonite through Multiscale! However, Celebi will have problems against Fighting-types, as it can't damage them quickly enough to defeat them, and many of them can OHKO in return.
The fourth slot is dedicated to a move to use against Steel-types. Hidden Power Fire is the best one, as the only Steel-type that don't fear Fire attacks is Heatran. Hidden Power Fire can quickly defeat Scizor, Ferrothorn, and Skarmory, all which are problematic if Celebi do not carry that move. However, Earth Power can be used instead. It has three advantages over Hidden Power Fire. The first is that it actually defeats Heatran. The second is that it is very useful against specially defensive Jirachi on rain, as it can take a boosted Hidden Power Fire if it's raining, paralyze Celebi, and take it out with repeated Iron Heads. The third is that it still can OHKO Scizor, but only after a Nasty Plot boost. However, Earth Power leaves Celebi helpless against any other Steel-type not weak to Ground, such as Skarmory, Bronzong, and Ferrothorn.
If you are using Psychic, is recommended that you use Hidden Power Fire, while if you run Earth Power, is recommended that you run Hidden Power Ice.
The EV spread maximizes Speed and Special Attack, letting Celebi tie with unboosted Volcarona, max speed Ninetales, and outspeed anything below it. If you are using Leftovers and the combination of Earth Power and Hidden Power Ice, another EV spread that can be used is 180 SpA / 84 SpD / 244 Spe. With that spread, Celebi can outspeed Modest Hydreigon, and OHKO it with a boosted Hidden Power Ice after Stealth Rock damage. With the Special Defense EVs, Celebi avoids the 2HKO from Hidden Power Ice from Sheer Force Landorus, and OHKO back with Hidden Power Ice, and this alone is reason to consider using this EV spread. Celebi can also avoid the 2HKO from non-Rain-boosted Specs Keldeo's Hydro Pump or the Scarf rain-boosted Hydro Pump, setup a Nasty Plot, and then OHKO back with Giga Drain, restoring all health lost on the process.
Generally, the recommended item is Life Orb. Leftovers can be used for a lot of reasons; it boosts Celebi's survivability a lot, especially on sandstorm teams, and guarantee that Sheer Force Landorus will have a hard time trying to 2HKO Celebi with Hidden Power Ice. However, Celebi loses out a lot of power. For example, even after a boost, Celebi can only OHKO 4/0 Dragonite after Stealth Rock damage. Also, Celebi misses out the OHKO on Hydreigon with +2 Hidden Power Ice, if Stealth Rock is not present on the field, and can never OHKO Scizor with +2 Earth Power after Stealth Rock damage. It also is not guaranteed to 2HKO physically defensive Skarmory with +2 Hidden Power Ice. For this reason, entry hazard support is more important than ever if you decide to use Leftovers.
Good Teammates:
Heatran resists all of Celebi's weakness and vice-versa. It can also deal better with Dragon-types and Steel-types than Celebi, thus, facilitating Celebi's work. Heatran can also deal with sun teams, which are problematic for Celebi. Celebi can then deal with the Fighting-types and sun teams that give problems to Heatran. These are reasons to why Heatran is generally the best partner to Celebi. Keldeo does a similar job to Heatran, although it doesn't have the same defensive synergy with Celebi, that Heatran has. Still, (especially on rain teams) Keldeo is an effective partner for Celebi, to facilitate its sweep. Tyranitar is another good partner, as it can take out Latios, Latias, and opposing Celebi, all of which give problems to Celebi. The latter also protects Tyranitar from rain teams. Specially Defensive Jirachi is another good partner, as it can spread paralysis to help Celebi's sweep, and can counter/check threats like Lati@s. Terrakion is another good partner. It takes the Fire-type attacks that give problems to Celebi, can wallbreak to facilitate Celebi's swep, can take out the pink blobs, and can revenge kill many things that give problems to Celebi, such as Tornadus.
What counters it:
Chansey and Blissey are the only foolproof counters to NP Celebi, as no matter which move Celebi runs, the pink blobs can easily sponge those moves, even when they are boosted. They are only 2HKOed by a +6 Giga Drain. Other counters to Celebi depend from which move it runs.
Heatran laughs at every other move that Celebi can use, but Earth Power will instantly murder him. However, Heatran can avoid Earth Power with an Air Balloon; take care of this fact. Specially Defensive Jirachi does a similar job if it is raining, as it avoids a 2HKO from a +2 Hidden Power Fire, and can paralyze Celebi, and take it out with repeated Iron Heads. However, like Heatran, it must avoid Earth Power, though Earth Power will only 2HKO specially defensive Jirachi, even at +2, so with a little of luck, it can still come out on the top. If Celebi lacks Hidden Power Fire, Skarmory, Bronzong, and Ferrothorn can counter Celebi very well. Note that physically defensive variants of Skarmory will be 2HKOed by a boosted Hidden Power Ice. Scizor will also pose problems if Celebi lacks Hidden Power Fire, or if it's raining, as Celebi will need a boost to, on the former situation, OHKO Scizor with Earth Power after Stealth Rock damage, and on the latter situation, simply OHKO Scizor (without Stealth Rock).
If Celebi lacks Hidden Power Ice, Lati@s and Hydreigon will pose problems, although even if Celebi has Hidden Power Ice, only Hydreigon can be reliably taken out, as both Lati@s can outspeed, and either avoid an OHKO, or outspeed and defeat Celebi with the apropriate move. Specially defensive versions of Dragonite are an annoyance to Celebi that lack Hidden Power Ice, as they avoid an OHKO from a boosted Psychic, and can either take Celebi down with Hurricane, or setup and OHKO with Outrage.
Although Celebi is hard to counter, there are some checks to it. Anything that can outspeed and hit with a Bug-type move or a super-effective STAB move will easily dispose of Celebi. These include Scarf Tyranitar, Terrakion (with X-Scissor), Scarf Scizor, physical variants of Landorus, Landorus-T, Scarf Heatran, and sun/chlorophyll sweepers in general. It should be noted that all of those threats cannot switch in, as they are in risk of being OHKOed by the appropriate move. It is always wise to scout Celebi's moves before attempting to revenge kill or knowing what you can use to wall him.

Celebi @ Life Orb / Leftovers
Trait: Natural Cure
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature (+SAtk, -Atk)
- Nasty Plot
- Giga Drain
- Psychic / Hidden Power [Ice]
- Hidden Power [Fire] / Earth Power
Role: Special Sweeper
What It Does: Now that Tornadus-T got banned, this set is even better than before. Now that Tornadus-T is banned, and not all Rain teams are going to use Tornadus, this set is a terror to rain teams, although it can also be good against other types of teams, such as Sun (when the sun is not shining, of course). This set takes advantage of the fact that the most common set to Celebi is Specially Defensive. Thus, many times, it can force Sheer Force (pun not inteded) Landorus, and Keldeo, out, and take advantage of this to setup a NP boost. Although Celebi is not that speedy, it has many advantages over other sweepers like RP Landorus. The first is that it has many good resistances to Fighting, Water, Ground, and Electric. The second is that Celebi is not weak to Stealth Rock. Also, should Celebi be statused, it can simply switch out to cure itself. Also, Celebi is weak to Ice Shard, although Mamoswine can never OHKO Celebi at full health, and will be OHKOed by Giga Drain in return. Celebi can also take Bullet Punch incredibly well, and resist Mach Punch and Aqua Jet althogether.
Nasty Plot boosts Celebi's Special Attack to incredible levels. The main sweeping move is Giga Drain. Although Grass isn't the best STAB to use offensively, as it is resisted by many types, it also hits Water- and Ground-types super-effectively. Plus, Giga Drain can heal Celebi, mitigating the Life Orb recoil.
The third slot goes to a move that Celebi will use against Dragon-types. Psychic is the recommended one, as it also receives STAB, and will have good neutral coverage against things that resist Giga Drain. Also, Psychic hits Fighting- and Poison-types super-effectively, and this is very important against teams that need a powerful weapon against Fighting-types. After a boost, Psychic is also able to OHKO most Dragon-types. Hidden Power Ice can be used instead. This is because Psychic needs a boost to be able to OHKO Dragon-types reliably, and Hidden Power Ice can do this without a boost. Also, Hidden Power Ice hits three Dragon-types that resist Psychic: Lati@s and Hydreigon. It also hits Landorus without having to resort to Psychic, as Sheer Force Landorus cannot OHKO this Celebi, but has a chance to 2HKO with Hidden Power Ice, but Celebi can't OHKO in return without Hidden Power Ice. Finally, Hidden Power Ice has a high chance, when boosted, to OHKO 4 / 0 Dragonite through Multiscale! However, Celebi will have problems against Fighting-types, as it can't damage them quickly enough to defeat them, and many of them can OHKO in return.
The fourth slot is dedicated to a move to use against Steel-types. Hidden Power Fire is the best one, as the only Steel-type that don't fear Fire attacks is Heatran. Hidden Power Fire can quickly defeat Scizor, Ferrothorn, and Skarmory, all which are problematic if Celebi do not carry that move. However, Earth Power can be used instead. It has three advantages over Hidden Power Fire. The first is that it actually defeats Heatran. The second is that it is very useful against specially defensive Jirachi on rain, as it can take a boosted Hidden Power Fire if it's raining, paralyze Celebi, and take it out with repeated Iron Heads. The third is that it still can OHKO Scizor, but only after a Nasty Plot boost. However, Earth Power leaves Celebi helpless against any other Steel-type not weak to Ground, such as Skarmory, Bronzong, and Ferrothorn.
If you are using Psychic, is recommended that you use Hidden Power Fire, while if you run Earth Power, is recommended that you run Hidden Power Ice.
The EV spread maximizes Speed and Special Attack, letting Celebi tie with unboosted Volcarona, max speed Ninetales, and outspeed anything below it. If you are using Leftovers and the combination of Earth Power and Hidden Power Ice, another EV spread that can be used is 180 SpA / 84 SpD / 244 Spe. With that spread, Celebi can outspeed Modest Hydreigon, and OHKO it with a boosted Hidden Power Ice after Stealth Rock damage. With the Special Defense EVs, Celebi avoids the 2HKO from Hidden Power Ice from Sheer Force Landorus, and OHKO back with Hidden Power Ice, and this alone is reason to consider using this EV spread. Celebi can also avoid the 2HKO from non-Rain-boosted Specs Keldeo's Hydro Pump or the Scarf rain-boosted Hydro Pump, setup a Nasty Plot, and then OHKO back with Giga Drain, restoring all health lost on the process.
Generally, the recommended item is Life Orb. Leftovers can be used for a lot of reasons; it boosts Celebi's survivability a lot, especially on sandstorm teams, and guarantee that Sheer Force Landorus will have a hard time trying to 2HKO Celebi with Hidden Power Ice. However, Celebi loses out a lot of power. For example, even after a boost, Celebi can only OHKO 4/0 Dragonite after Stealth Rock damage. Also, Celebi misses out the OHKO on Hydreigon with +2 Hidden Power Ice, if Stealth Rock is not present on the field, and can never OHKO Scizor with +2 Earth Power after Stealth Rock damage. It also is not guaranteed to 2HKO physically defensive Skarmory with +2 Hidden Power Ice. For this reason, entry hazard support is more important than ever if you decide to use Leftovers.
Good Teammates:
Heatran resists all of Celebi's weakness and vice-versa. It can also deal better with Dragon-types and Steel-types than Celebi, thus, facilitating Celebi's work. Heatran can also deal with sun teams, which are problematic for Celebi. Celebi can then deal with the Fighting-types and sun teams that give problems to Heatran. These are reasons to why Heatran is generally the best partner to Celebi. Keldeo does a similar job to Heatran, although it doesn't have the same defensive synergy with Celebi, that Heatran has. Still, (especially on rain teams) Keldeo is an effective partner for Celebi, to facilitate its sweep. Tyranitar is another good partner, as it can take out Latios, Latias, and opposing Celebi, all of which give problems to Celebi. The latter also protects Tyranitar from rain teams. Specially Defensive Jirachi is another good partner, as it can spread paralysis to help Celebi's sweep, and can counter/check threats like Lati@s. Terrakion is another good partner. It takes the Fire-type attacks that give problems to Celebi, can wallbreak to facilitate Celebi's swep, can take out the pink blobs, and can revenge kill many things that give problems to Celebi, such as Tornadus.
What counters it:
Chansey and Blissey are the only foolproof counters to NP Celebi, as no matter which move Celebi runs, the pink blobs can easily sponge those moves, even when they are boosted. They are only 2HKOed by a +6 Giga Drain. Other counters to Celebi depend from which move it runs.
Heatran laughs at every other move that Celebi can use, but Earth Power will instantly murder him. However, Heatran can avoid Earth Power with an Air Balloon; take care of this fact. Specially Defensive Jirachi does a similar job if it is raining, as it avoids a 2HKO from a +2 Hidden Power Fire, and can paralyze Celebi, and take it out with repeated Iron Heads. However, like Heatran, it must avoid Earth Power, though Earth Power will only 2HKO specially defensive Jirachi, even at +2, so with a little of luck, it can still come out on the top. If Celebi lacks Hidden Power Fire, Skarmory, Bronzong, and Ferrothorn can counter Celebi very well. Note that physically defensive variants of Skarmory will be 2HKOed by a boosted Hidden Power Ice. Scizor will also pose problems if Celebi lacks Hidden Power Fire, or if it's raining, as Celebi will need a boost to, on the former situation, OHKO Scizor with Earth Power after Stealth Rock damage, and on the latter situation, simply OHKO Scizor (without Stealth Rock).
If Celebi lacks Hidden Power Ice, Lati@s and Hydreigon will pose problems, although even if Celebi has Hidden Power Ice, only Hydreigon can be reliably taken out, as both Lati@s can outspeed, and either avoid an OHKO, or outspeed and defeat Celebi with the apropriate move. Specially defensive versions of Dragonite are an annoyance to Celebi that lack Hidden Power Ice, as they avoid an OHKO from a boosted Psychic, and can either take Celebi down with Hurricane, or setup and OHKO with Outrage.
Although Celebi is hard to counter, there are some checks to it. Anything that can outspeed and hit with a Bug-type move or a super-effective STAB move will easily dispose of Celebi. These include Scarf Tyranitar, Terrakion (with X-Scissor), Scarf Scizor, physical variants of Landorus, Landorus-T, Scarf Heatran, and sun/chlorophyll sweepers in general. It should be noted that all of those threats cannot switch in, as they are in risk of being OHKOed by the appropriate move. It is always wise to scout Celebi's moves before attempting to revenge kill or knowing what you can use to wall him.