This is my calling :)
Threats:
Charizard @ Charizardite Y
Ability: Blaze / Solar Power
EVs: 252 SpA / 4 SpD / 252 Spe
Modest / Timid Nature
- Fire Blast
- Solar Beam
- Focus Blast
- Roost / Dragon Pulse
Charizard-Y forces out Ferrothorn with its STAB and also KOs Jellicent with the combination of sun-boosted Fire Blast and Solar Beam after rocks regardless of nature. It is a very powerful attacker in general. Solar Power is situational, but Solar Power-boosted base Charizard is more powerful than Mega Charizard Y due to it being an effective Choice Specs boost, making it cool if you don't mind risking Zard taking a little damage on one or two of its attacks.
252 SpA Mega Charizard Y Fire Blast vs. 248 HP / 172+ SpD Jellicent in Sun: 117-138 (29 - 34.2%) -- 99.4% chance to 4HKO after Leftovers recovery
252 SpA Mega Charizard Y Solar Beam vs. 248 HP / 172+ SpD Jellicent: 226-268 (56 - 66.5%) -- guaranteed 2HKO after Leftovers recovery
12.5%+29%+56%=97.5%
Magnezone @ Choice Specs
Ability: Magnet Pull
EVs: 128 HP / 252 SpA / 128 Spe
Modest Nature
- Thunderbolt
- Volt Switch
- Flash Cannon
- Hidden Power Fire
Magnezone does a number on this core, trapping and OHKOing Ferrothorn with HP Fire and also dealing heavy damage to Jellicent with its choice of Thunderbolt or Volt Switch. Do note, however, that Jellicent is such a specially defensive monster that T-Bolt can't guarantee the OHKO on it from full health and that it can predict a Volt Switch in a pinch if it is at full health and use Recover to stay at healthy after a Volt Switch, which is just evidence that people have been sleeping on this thing for way too long
252+ SpA Choice Specs Magnezone Thunderbolt vs. 248 HP / 172+ SpD Jellicent: 360-426 (89.3 - 105.7%) -- 31.3% chance to OHKO
252+ SpA Choice Specs Magnezone Hidden Power Fire vs. 252 HP / 168 SpD Ferrothorn: 332-392 (94.3 - 111.3%) -- guaranteed OHKO after Stealth Rock
As an aside, please take note of the fact that 44 spe variants of Jellicent only have a 12.5% chance of being OHKOed while max/max variants have a 25% chance to avoid an OHKO it after rocks. Jellicent is insanely fat on the special side :D
Partners:
Heatran @ Leftovers
Ability: Flash Fire
EVs: 252 HP / 4 SpA / 252 Spe OR 252 HP / 188 SpD / 68 Spe
Timid / Calm Nature
- Lava Plume
- Stealth Rock
- Toxic
- Protect / Roar
Please for the love of god don't run Calm with the first spread and please for the love of god don't run Timid with the second spread. Anyway, I've talked about Ferro+utility Tran+Jellicent before in the old good cores thread, and I'm not gonna elaborate too much as the post I made after innovating it (which can be found here) covers just about everything you need to know about this three-mon core. A tl;dr of that post is as follows: FWG, stacks hazards, absorbs Fire-type moves for Ferrothorn, Jelly absorbs scalds and spinblocks, Ferro improves Tran's longevity with Leech Seed.
Talonflame @ Leftovers
Ability: Gale Wings / Flame Body (shoutouts to Clair)
EVs: 248 HP / 252 SpD / 8 Spe OR 248 HP / 252 Def / 8 Spe
Careful / Impish Nature
- Brave Bird
- Bulk Up / Taunt
- Will-O-Wisp
- Roost
This forms an FWG core and is able to just kinda 6:0 certain teams with Bulk Up while just generally being a good backup stallbreaker for Jellicent. The synergy is good, with it cockblocking Grass-types outside of (Rock Slide/Ancient Power/HP Rock lures) for Jellicent and covering Fire-types for Ferrothorn in exchange for them both covering waters and Ferrothorn covering Rock-types and Electric-types barring Manectric and Magnezone (although both of these can be stalled with Roosts if Gale Wings is used as well as being caught on the switch by Wisp, waring them down while stalling). PhysDef Talon is a very underrated set considering what it checks, which is why I've slashed it in, and either SpD or PhysDef with Flame Body (as innovated by the god Clair in puppet theatre) just kinda shits on a lot of stall builds, although I wouldn't run it with Bulk Up as imo Bulk Up is too reliant on Gale Wings to retain the offense matchup+longevity by comparison to Taunt+Wisp.
Stunfisk @ Rocky Helmet
Ability: Static
EVs: 44 HP / 224 Def / 240 SpD
Bold Nature
- Discharge
- Earth Power
- Stealth Rock
- Yawn / Pain Split / Toxic / Scald
The lord himself makes for a glorious core with this twosome. It cockblocks Electric-types--namely including Magnezone and Manectric, who both shit on this core--provides role stacking with Ferrothorn by punishing contact moves with the core of Iron Barbs Ferro and Helmet+Static Stunfisk, and with it providing hazard stacking alongside Jellicent the master spinblocker and Ferrothorn the spiky lord. In addition, Scald allows it to lure out deal decent damage to and potentially burn Lando-T, which is useful considering that SD variants do a number on this core. Normally I'm not big on Scald Fisk, but here it is definitely useful. In exchange, Ferrothorn covers PhysDef SD-less Lando-T and Grass-types for Stunfisk, Jellicent eases certain matchups for Fisk with its own Scald and Wisp and both Jellicent and Ferro cover Water-types nicely.
Threats:

Charizard @ Charizardite Y
Ability: Blaze / Solar Power
EVs: 252 SpA / 4 SpD / 252 Spe
Modest / Timid Nature
- Fire Blast
- Solar Beam
- Focus Blast
- Roost / Dragon Pulse
Charizard-Y forces out Ferrothorn with its STAB and also KOs Jellicent with the combination of sun-boosted Fire Blast and Solar Beam after rocks regardless of nature. It is a very powerful attacker in general. Solar Power is situational, but Solar Power-boosted base Charizard is more powerful than Mega Charizard Y due to it being an effective Choice Specs boost, making it cool if you don't mind risking Zard taking a little damage on one or two of its attacks.
252 SpA Mega Charizard Y Fire Blast vs. 248 HP / 172+ SpD Jellicent in Sun: 117-138 (29 - 34.2%) -- 99.4% chance to 4HKO after Leftovers recovery
252 SpA Mega Charizard Y Solar Beam vs. 248 HP / 172+ SpD Jellicent: 226-268 (56 - 66.5%) -- guaranteed 2HKO after Leftovers recovery
12.5%+29%+56%=97.5%

Magnezone @ Choice Specs
Ability: Magnet Pull
EVs: 128 HP / 252 SpA / 128 Spe
Modest Nature
- Thunderbolt
- Volt Switch
- Flash Cannon
- Hidden Power Fire
Magnezone does a number on this core, trapping and OHKOing Ferrothorn with HP Fire and also dealing heavy damage to Jellicent with its choice of Thunderbolt or Volt Switch. Do note, however, that Jellicent is such a specially defensive monster that T-Bolt can't guarantee the OHKO on it from full health and that it can predict a Volt Switch in a pinch if it is at full health and use Recover to stay at healthy after a Volt Switch, which is just evidence that people have been sleeping on this thing for way too long
252+ SpA Choice Specs Magnezone Thunderbolt vs. 248 HP / 172+ SpD Jellicent: 360-426 (89.3 - 105.7%) -- 31.3% chance to OHKO
252+ SpA Choice Specs Magnezone Hidden Power Fire vs. 252 HP / 168 SpD Ferrothorn: 332-392 (94.3 - 111.3%) -- guaranteed OHKO after Stealth Rock
As an aside, please take note of the fact that 44 spe variants of Jellicent only have a 12.5% chance of being OHKOed while max/max variants have a 25% chance to avoid an OHKO it after rocks. Jellicent is insanely fat on the special side :D
Partners:

Heatran @ Leftovers
Ability: Flash Fire
EVs: 252 HP / 4 SpA / 252 Spe OR 252 HP / 188 SpD / 68 Spe
Timid / Calm Nature
- Lava Plume
- Stealth Rock
- Toxic
- Protect / Roar
Please for the love of god don't run Calm with the first spread and please for the love of god don't run Timid with the second spread. Anyway, I've talked about Ferro+utility Tran+Jellicent before in the old good cores thread, and I'm not gonna elaborate too much as the post I made after innovating it (which can be found here) covers just about everything you need to know about this three-mon core. A tl;dr of that post is as follows: FWG, stacks hazards, absorbs Fire-type moves for Ferrothorn, Jelly absorbs scalds and spinblocks, Ferro improves Tran's longevity with Leech Seed.

Talonflame @ Leftovers
Ability: Gale Wings / Flame Body (shoutouts to Clair)
EVs: 248 HP / 252 SpD / 8 Spe OR 248 HP / 252 Def / 8 Spe
Careful / Impish Nature
- Brave Bird
- Bulk Up / Taunt
- Will-O-Wisp
- Roost
This forms an FWG core and is able to just kinda 6:0 certain teams with Bulk Up while just generally being a good backup stallbreaker for Jellicent. The synergy is good, with it cockblocking Grass-types outside of (Rock Slide/Ancient Power/HP Rock lures) for Jellicent and covering Fire-types for Ferrothorn in exchange for them both covering waters and Ferrothorn covering Rock-types and Electric-types barring Manectric and Magnezone (although both of these can be stalled with Roosts if Gale Wings is used as well as being caught on the switch by Wisp, waring them down while stalling). PhysDef Talon is a very underrated set considering what it checks, which is why I've slashed it in, and either SpD or PhysDef with Flame Body (as innovated by the god Clair in puppet theatre) just kinda shits on a lot of stall builds, although I wouldn't run it with Bulk Up as imo Bulk Up is too reliant on Gale Wings to retain the offense matchup+longevity by comparison to Taunt+Wisp.

Stunfisk @ Rocky Helmet
Ability: Static
EVs: 44 HP / 224 Def / 240 SpD
Bold Nature
- Discharge
- Earth Power
- Stealth Rock
- Yawn / Pain Split / Toxic / Scald
The lord himself makes for a glorious core with this twosome. It cockblocks Electric-types--namely including Magnezone and Manectric, who both shit on this core--provides role stacking with Ferrothorn by punishing contact moves with the core of Iron Barbs Ferro and Helmet+Static Stunfisk, and with it providing hazard stacking alongside Jellicent the master spinblocker and Ferrothorn the spiky lord. In addition, Scald allows it to lure out deal decent damage to and potentially burn Lando-T, which is useful considering that SD variants do a number on this core. Normally I'm not big on Scald Fisk, but here it is definitely useful. In exchange, Ferrothorn covers PhysDef SD-less Lando-T and Grass-types for Stunfisk, Jellicent eases certain matchups for Fisk with its own Scald and Wisp and both Jellicent and Ferro cover Water-types nicely.
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