Magnezone @ Air Balloon
Ability: Magnet Pull
EVs: 4 Def/252 SpA/252 Spe
Modest Nature
Tera-Type: Flying/Ground
- Thunder Bolt/Tera Blast
- Volt Switch
- Flash Cannon
- Iron Defense
From memory, the main Magnezone you come across (if you do at all) is a Choice-locked Zone of some variation; Scarf to patch up its mediocre level of speed, or Specs to break physical walls (especially bulky Waters). Great Tusk can easily come in on Zone with a predicted Electric attack (which it's immune to because Ground-type), and cleanly OHKO Zone with STAB EQ because x4 weakness. It might have to watch for Specs Flash Cannon, but it can take one if it's at full health
and it comes in safely. And chances are, the damage it ultimately took would be worth the kill on Zone.
In any case, the idea here is that you Iron Defense with Zone as Tusk comes in to block the expected Volt Switch. Between the intact Balloon and the +2 Defense, Great Tusk theoretically never kills it in one shot, not even if it runs Body Press as a back-up move.
252+ Def Great Tusk Body Press vs. +2 0 HP / 4 Def Magnezone: 128-152 (45.5 - 54%) -- 39.1% chance to 2HKO
This in turn allows Zone to 2HKO Tusk with Flash Cannon. The important distinction here is that Modest Zone secures the 2HKO without the need for hazards to have been tossed down beforehand. Timid Zone does not.
Modest Calc: 252+ SpA Magnezone Flash Cannon vs. 252 HP / 4 SpD Great Tusk: 237-280 (54.6 - 64.5%) -- guaranteed 2HKO after Leftovers recovery
Timid Calc: 252 SpA Magnezone Flash Cannon vs. 252 HP / 4 SpD Great Tusk: 216-255 (49.7 - 58.7%) -- 69.5% chance to 2HKO after Leftovers recovery
Thankfully, in this situation Tusk decided to be fat and slow, giving Zone the capability to outspeed it even
with the Modest nature. You might still wanna stick with the 252EVs in Speed just to be safe, though; there might be base 90 speed mons that decide to fully invest in bulk instead for whatever reason, and the extra Def EVs you'd need to guarantee the survival against Tusk's EQ might not be worth underspeeding those mons in particular.
Tera-Flying allows both it
and the Balloon to failsafe each other. The Balloon covers for the scenario in which you burned your ability to Terastillaze already, and Tera-Flying covers for the admittedly likely event that the Balloon gets popped prematurely, whether by a faster Volt-Turner or otherwise. You don't necessarily have to Terastallize this Zone for the fight against Tusk if you don't want to, especially not if you can keep it healthy. Overall, I'd say it's only semi-reliant at worst, although I wouldn't mind having it as a back-up plan.
Tera Blast is slashed in the side of Thunder Bolt on the off-chance you want Zone to be your designated Tera mon, and it's over T-Bolt because Volt Switch is the more important of the two Electric STABs to keep, due to the momentum that it gives to Zone. Note that if you do decide to use Tera Blast, it'd be wise to swap Zone's Tera-Type to Ground so that it can better combat the Steels it's meant to trap, as well as opposing Electrics which otherwise wall it to buggery.
Speaking of Terastallization, the beauty about Zone luring Tusk is that it also actually discourages Tusk from Terastallizing
against it. Reasoning should be obvious: if it was Tera-Water, it'd get nuked by Zone's T-Bolt, and if it was Steel, it'd get trapped by the very thing it arrogantly thought it could switch in on! I dunno about you guys, but I personally think that's amazing; not to mention ironic.
I considered Chople Berry & Magnet Rise in place of ID/Balloon as well, but there was a chance that Tusk would bail right from the start if it saw Magnet Rise in effect; that chance would be greater if it lacked any Fighting STAB to begin with. With ID/Balloon, you're guaranteed to at least take that first chunk off Tusk while it Spins to pop the balloon, or Knocks if it realizes the following EQ would be a roll with the +2 Defense up.