Depending on what Jean does, there is a very small chance that PGP will be frozen solid on Turn One. If this happens, Dirk will resign. Immediately. He won't even comment, he'll just flag his resignation and walk. Jean is free to try and find him later, the press is free to find him later, but the answer he'll give is "Didn't feel like it."
Okay, with that contingency out of the way, it's time for strategy.
Versus Jean, it's back to basics. Dirk's turn one move for PGP is Trick Room. He's mostly hoping that Jean will either switch on that turn or use Earthquake. As usual, Porygon2 with Eviolite is just not a OHKO kind of target, so unless Mamoswine causes a Flinch or Freezes PGP solid, he'll get his Trick Room up smoothly. If PGP flinches, he'll just try again. In any case, what happens after Trick Room is up depends on who Jean has on the field.
If Mamoswine is still on the field, PGP's first move after setting up Trick Room will be Magnet Rise. Dirk knows how Jean feels about Magnet Rise normally, and he is hoping to spook Jean into a switch. With that in mind, after Magnet Rise, PGP will use Recover--in other words, he's hoping to get a free heal turn while Jean switches. If Jean does switch, see the next strategy bulletpoint. If not, PGP will use Tri Attack. Because Mamoswine's Special Defence is lower than its defence, PGP's Special Attack rose one stage on the first turn. Combined with the 1.5x STAB boost, Tri Attack is a surprisingly solid move with decent odds of inflicting status, for extra fun. At this point, Dirk will recall PGP manually, and send out Heraclitus the Arctovish. With Magnet Rise active, Jean is extremely unlikely to use Earthquake, so Arctovish might be fortunate enough to swap in on an ice move. If not, Arctovish is bulky enough to take an Earthquake (probably) and set up on Mamoswine with Whirlpool. Wait, what? Yes. Whirlpool. Super-effective trapping move.
Because by now, Trick Room has run out and it's time to get PGP back in, but Dirk isn't taking any chances. So he recalls Arctovish and sends out Yolkai. If he's lucky and guessed right, Jean will be using... not an ice move, basically. If he's really lucky, Yolkai will survive that round and use Explosion. Which might legit KO Mamoswine, tbh. Anyway, whether or not Yolkai doesn't survive because Mamoswine KO'd her, or Explosion doesn't KO Mamoswine (but with the Tri Attack and cumulative Whirlpool damage...)
...at any rate, Yolkai has fainted and PGP is back, not at full HP but probably doing pretty well all things considered. If Mamoswine is really low, Dirk might just have PGP use Recover and see if Whirlpool finishes Mamoswine off, but if not... it's time for Trick Room again. Mamoswine is still trapped, and still taking Whirlpool damage. At which point things depend on whether or not PGP survives the round. If so, then... yeah, it uses Tri Attack. Get outta here, Mamoswine.
If Jean switched at the beginning, though, this gets even easier. Presumably Jean won't switch to Gyarados, but if he does, PGP has Discharge. Which... like. That sucks for Jean, but this is a digital drinky bird that has previously proven capable of using Zap Cannon. So, maybe this is what "play stupid games, win stupid prizes" means. (Actually, interacting with Dirk Strider is a stupid game and every prize for it is stupid. How was he allowed to get this far. Why isn't he being chased off the field by the Moms Against Dirk. They're definitely in the stands, holding signs and booing him. He thinks this is great.)
So, uh, probably that won't happen? Maybe Jean swaps instead to Hydreigon. This is where things get kind of extra unfair. Because PGP has Ice Beam. So no matter who Jean swaps in on PGP, PGP has something super-effective, and the advantage of the first turn. This is basically what Trick Room was made for.
It's possible, of course, that Jean will send out one of these Pokemon and then swap for another, wasting Dirk's Trick Room turns and generally racking up smaller amounts of damage on his own team instead of getting hit with super-effective blows. If this happens, Dirk will allow it, because none of the Abilities of Jean's Pokemon are going to hurt PGP's sweep very much. Once Mamoswine is down, what Dirk does next will depend entirely on who Jean sends out.
We shall assume, for the sake of everyone's sanity, that Trick Room has run out now and this next leg of strategy is a "new rotation."
(Unless, of course, Mamoswine really took that long to KO, in which case PGP has a couple more rounds of Trick Room up.)
The first thing Dirk will do regardless of circumstance is set up Trick Room. He does not care if this gives Hydreigon a chance for Nasty Plot, or Work Up, or whatever. He does not care if PGP gets hit with a Flinch inducing move like Bite or Headbutt. Those are small fry amounts of damage, and easily Recovered from. Dragon Rush would suck a bit more, but that is still irrelevant, he needs Trick Room up.
If, at any point, Jean swaps to Gyarados: if he's lucky, he'll swap in on a Water type move, activating Water Absorb to heal Arctovish, who can then then use Hail and then Aurora Veil for some added longevity so it can Freeze Dry (with STAB bonus!) the living daylights out of Gyarados. Until this moment, Arctovish's Ability has been pretty much secret, so maybe it'll happen. If Gyarados somehow KOs Arctovish, PGP has Discharge, and now its Eviolite-boosted defences are further bolstered by the effects of Aurora Veil. But he's really not expecting much from this, because even if this was meant to fake Dirk out, Freeze Dry is also super effective on Hydreigon. The only difference is that Dirk would prefer to be using Icicle Crash on Hydreigon if he's got Arctovish out. The Flinch chance (and higher Attack stat on Arctovish) make a big difference sometimes.
Really, at this point, both PGP and Arctovish are equipped with super-effective moves against Jean's remaining Pokemon. PGP's Recover heals fully half its HP, and unless Jean gets very lucky with status/flinching, he doesn't have much to prevent Dirk from sweeping him.
Unless, of course, he freezes PGP first turn. Then Dirk walks away. He's petty like that.
Dirk and the Toon Squad
Okay, with that contingency out of the way, it's time for strategy.
Versus Jean, it's back to basics. Dirk's turn one move for PGP is Trick Room. He's mostly hoping that Jean will either switch on that turn or use Earthquake. As usual, Porygon2 with Eviolite is just not a OHKO kind of target, so unless Mamoswine causes a Flinch or Freezes PGP solid, he'll get his Trick Room up smoothly. If PGP flinches, he'll just try again. In any case, what happens after Trick Room is up depends on who Jean has on the field.
If Mamoswine is still on the field, PGP's first move after setting up Trick Room will be Magnet Rise. Dirk knows how Jean feels about Magnet Rise normally, and he is hoping to spook Jean into a switch. With that in mind, after Magnet Rise, PGP will use Recover--in other words, he's hoping to get a free heal turn while Jean switches. If Jean does switch, see the next strategy bulletpoint. If not, PGP will use Tri Attack. Because Mamoswine's Special Defence is lower than its defence, PGP's Special Attack rose one stage on the first turn. Combined with the 1.5x STAB boost, Tri Attack is a surprisingly solid move with decent odds of inflicting status, for extra fun. At this point, Dirk will recall PGP manually, and send out Heraclitus the Arctovish. With Magnet Rise active, Jean is extremely unlikely to use Earthquake, so Arctovish might be fortunate enough to swap in on an ice move. If not, Arctovish is bulky enough to take an Earthquake (probably) and set up on Mamoswine with Whirlpool. Wait, what? Yes. Whirlpool. Super-effective trapping move.
Because by now, Trick Room has run out and it's time to get PGP back in, but Dirk isn't taking any chances. So he recalls Arctovish and sends out Yolkai. If he's lucky and guessed right, Jean will be using... not an ice move, basically. If he's really lucky, Yolkai will survive that round and use Explosion. Which might legit KO Mamoswine, tbh. Anyway, whether or not Yolkai doesn't survive because Mamoswine KO'd her, or Explosion doesn't KO Mamoswine (but with the Tri Attack and cumulative Whirlpool damage...)
...at any rate, Yolkai has fainted and PGP is back, not at full HP but probably doing pretty well all things considered. If Mamoswine is really low, Dirk might just have PGP use Recover and see if Whirlpool finishes Mamoswine off, but if not... it's time for Trick Room again. Mamoswine is still trapped, and still taking Whirlpool damage. At which point things depend on whether or not PGP survives the round. If so, then... yeah, it uses Tri Attack. Get outta here, Mamoswine.
If Jean switched at the beginning, though, this gets even easier. Presumably Jean won't switch to Gyarados, but if he does, PGP has Discharge. Which... like. That sucks for Jean, but this is a digital drinky bird that has previously proven capable of using Zap Cannon. So, maybe this is what "play stupid games, win stupid prizes" means. (Actually, interacting with Dirk Strider is a stupid game and every prize for it is stupid. How was he allowed to get this far. Why isn't he being chased off the field by the Moms Against Dirk. They're definitely in the stands, holding signs and booing him. He thinks this is great.)
So, uh, probably that won't happen? Maybe Jean swaps instead to Hydreigon. This is where things get kind of extra unfair. Because PGP has Ice Beam. So no matter who Jean swaps in on PGP, PGP has something super-effective, and the advantage of the first turn. This is basically what Trick Room was made for.
It's possible, of course, that Jean will send out one of these Pokemon and then swap for another, wasting Dirk's Trick Room turns and generally racking up smaller amounts of damage on his own team instead of getting hit with super-effective blows. If this happens, Dirk will allow it, because none of the Abilities of Jean's Pokemon are going to hurt PGP's sweep very much. Once Mamoswine is down, what Dirk does next will depend entirely on who Jean sends out.
We shall assume, for the sake of everyone's sanity, that Trick Room has run out now and this next leg of strategy is a "new rotation."
(Unless, of course, Mamoswine really took that long to KO, in which case PGP has a couple more rounds of Trick Room up.)
The first thing Dirk will do regardless of circumstance is set up Trick Room. He does not care if this gives Hydreigon a chance for Nasty Plot, or Work Up, or whatever. He does not care if PGP gets hit with a Flinch inducing move like Bite or Headbutt. Those are small fry amounts of damage, and easily Recovered from. Dragon Rush would suck a bit more, but that is still irrelevant, he needs Trick Room up.
If, at any point, Jean swaps to Gyarados: if he's lucky, he'll swap in on a Water type move, activating Water Absorb to heal Arctovish, who can then then use Hail and then Aurora Veil for some added longevity so it can Freeze Dry (with STAB bonus!) the living daylights out of Gyarados. Until this moment, Arctovish's Ability has been pretty much secret, so maybe it'll happen. If Gyarados somehow KOs Arctovish, PGP has Discharge, and now its Eviolite-boosted defences are further bolstered by the effects of Aurora Veil. But he's really not expecting much from this, because even if this was meant to fake Dirk out, Freeze Dry is also super effective on Hydreigon. The only difference is that Dirk would prefer to be using Icicle Crash on Hydreigon if he's got Arctovish out. The Flinch chance (and higher Attack stat on Arctovish) make a big difference sometimes.
Really, at this point, both PGP and Arctovish are equipped with super-effective moves against Jean's remaining Pokemon. PGP's Recover heals fully half its HP, and unless Jean gets very lucky with status/flinching, he doesn't have much to prevent Dirk from sweeping him.
Unless, of course, he freezes PGP first turn. Then Dirk walks away. He's petty like that.