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Heyyyy... sooo.... hypothetically speaking, if I were to to accept your challenge in the Battle Tower with Milotic and Kecleon, who might I expect you to use......?
Air Balloon's description is apparently different in ASB (I was really sure it wasn't!).
"This item does not interfere with the Pokemon using any of its attacks and is consumed when the Pokemon takes 25% of its maximum HP in damage." 25% of 90 would be 22.5 ~ 23 HP so I'm thinking that's when it would be popping.
Are you interpreting the description in another way (it could be 23 HP away from 90 HP so it would pop at 67 HP but I'm not sure about that)? Because it just seems pretty strange.