At first glance, it might seem like Simisage has almost no advantages over other NU Grass-types, being less powerful than some, such as Exeggutor, and slower than others such as Serperior. However, Simisage has useful tools that help it preform in the NU tier and make it worth using over other Grass-types. A useful base 101 Speed and access to Nasty Plot make it an effective sweeper, and a fast Leaf Storm backed up by its decent Special Attack can really put the hurt on the opponent. It also has access to Focus Blast, which helps it get past Steel-type Pokemon, as well as destroying Sap Sipper Sawsbuck and Miltank, which are immune to Grass-type moves.
Despite this, Simisage has very notable flaws beyond simply having competition. Grass is a bad STAB to have in a metagame filled with Pokemon that resist it such as Braviary, Vileplume, and Skuntank. In addition, Simisage will not be taking hits very well, as it is pretty frail and has a mediocre defensive typing. However, despite these drawbacks, if you have the right support, Simisage is a Pokemon to consider for your team.
With a plethora of special attacks, Simisage is a good candidate for a special sweeper. This set either does one of two things depending on the first move choice. With Nasty Plot, it can increase its Special Attack and get the chance to sweep the foe, while with Leaf Storm, it can fire off a very powerful move and then run. Note that a Leaf Storm hits nearly as hard as a +2 Giga Drain without requiring any set up, but the choice is primarily up to the user.
Giga Drain is your main STAB with Nasty Plot or your alternative STAB with Leaf Storm. Despite its relatively low Base Power, the ability to heal Life Orb damage while also dealing a decent amount of damage makes it a useful move regardless. While Grass isn't a great STAB within the NU tier, Simisage has useful coverage moves to hit what its STAB cannot. Steel-types are easily taken down with Focus Blast, especially if they have a 4x weakness to the move like Probopass and Bastiodon. It also steamrolls Sawsbuck and Miltank, OHKOing Sawsbuck easily and doing a minimum of 70.56% to even the bulkiest of Miltank. Hidden Power Ice is the recommended choice for the final slot as it gets past Vileplume, which otherwise almost completely walls Simisage. It also hits Altaria harder than any other move Simisage has. Hidden Power Rock is a solid alternative to hit Fire-type Pokemon, most notably Charizard, hard. Note that both options hit Flying-types like Braviary for super effective damage.Team Options & Additional Comments >>>
This set is built to force a Pokemon that Simisage threatens out and set up a Substitute, then to take advantage of Simisage's solid coverage and high Speed. With the release of Overgrow, Simisage pulls this set off much better than its only real competition, Serperior. It has extra coverage with Superpower and is significantly stronger than Serperior, flaunting the ability to OHKO 4/0 Samurott without needing Overgrow active. Unlike Serperior, Simisage is slower than Scolipede—which seems like it could be an issue, but Simisage can set up a Substitute on the switch-in and OHKO the incoming Scolipede with Hidden Power Rock after Stealth Rock damage. Simisage actually finds quite a number of opportunities to set up a Substitute despite its mediocre bulk, since many Rock-, Ground-, and Water-type Pokemon won't even bother trying to stay in on Simisage, giving you a free turn to do so. Using Substitute and Life Orb together might seem like a bad idea because they both rack up self inflicted damage, but it gives Simisage the ability to easily manipulate its remaining HP and push itself into Overgrow range if it needs the power for the next attack. Substitute also allows it to evade Sucker Punch from the likes of Skuntank and Cacturne, though you probably don't want to stay in on the former if you can avoid it.
When in Overgrow range, Giga Drain packs a surprising amount of power and allows Simisage to make up for the recoil from Life Orb and Substitute. Superpower provides coverage on Steel-types as well as hitting most Grass- and Dragon-types neutrally. It also nails Skuntank, who is a pain in the rear to deal with when Simisage lacks Superpower. Superpower is used instead of Focus Blast because it allows Simisage to 2HKO Regice and Lickilicky on the switch and because it's actually accurate (after all, who actually likes using Focus Blast?). Hidden Power Rock OHKOes Scolipede after Stealth Rock damage, and covers pesky Fire- and Flying-types that resist Simisage's STAB. This set performs admirably mid- to late-game, especially once entry hazards have been set up, since Simisage can punch through nearly all of its checks after some hazard damage.Team Options & Additional Comments >>>
Simisage has a good amount of other options to consider. A set with Substitute over Leaf Storm and Nasty Plot can be used with Overgrow, similarly to Sceptile in RU. Another similarity between it and Sceptile is that Simisage has Leech Seed, which can be used for a SubSeed set. However, Exeggutor is usually a better choice, as with Harvest, it will usually heal a lot more than Simisage, and its additional Psychic typing puts more pressure on the opponent to allow it to set up. Synthesis is useful for free healing, and with Taunt, it can make Simisage an effective stallbreaker, but most of the time Simisage will find itself far too frail to accomplish this. Because it has Gluttony, a Petaya or Salac Berry is an acceptable option as they will activate early on. Simisage has a surprisingly large physical movepool, containing goodies such as Seed Bomb, Low Kick, Superpower, Rock Slide, Acrobatics, and Crunch. However, with only Work Up to boost its average Attack stat and with a mediocre STAB, you are usually better off finding something else to function as a physical attacker.
Checks and Counters
If Simisage gets a Nasty Plot boost, it can be a pain to take down, but usually defeating it isn't that difficult. Poison-types such as Skuntank, Muk, and Garbodor are among the best options, as they have good bulk and other than Skuntank resist all its moves besides Hidden Power. From there, all of them can either OHKO Simisage with their Poison STABs, or Garbodor can set up Spikes against it. Vileplume can be OHKOed by a Hidden Power Ice at +2 after Stealth Rock, but is otherwise an even better option than other Poison-types due to its 4x resistance to Grass. Specially defensive Ludicolo can take on Simisage's onslaughts well and do massive damage with an Ice Beam. Combusken can easily OHKO and isn't weak to either Hidden Power, but note that a +2 Focus Blast OHKOes. Substitute + Bulk Up Braviary can use Simisage as setup fodder if Simisage has a Special Attack drop due to Leaf Storm. If Simisage is running Hidden Power Ice, Flareon and Charizard can take hits from it well and retaliate with their Fire STAB. Choice Scarf Rotom-S can switch into a Grass-type move and retaliate with Air Slash. There are many, many revenge killers that cannot switch in, such as Swellow, which easily OHKO Simisage due to its frailty.