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Jiggs has much more HP than ditto and I'm pretty sure choice scarf does affect gyro ball (I can't find a good source on it though)
Edit: Jiggs probably also had eviolite
If it d-dances you go for encore, or if you don't have encore, you could taunt it to stop it from d-dancing or roosting in the first place (zekrom needs two d-dances to beat xerneas while burned).
Or you know, you burn it:
252+ Atk Choice Band Tough Claws burned Zekrom Thunder Punch vs. 252 HP / 252+ Def Xerneas: 111-132 (24.3 - 28.9%) -- 59.2% chance to 4HKO after Stealth Rock and Leftovers recovery
Terrakion is pretty cool here
Malamar (Terrakion) @ Leftovers
Ability: Contrary
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Superpower
- Knock Off
- Rock Slide
- Substitute
Get a substitute up and then spam superpower. Knock off is for ghost types and rock slide is for flying types and...