Can you play Gust targeting an 8 Might unit as Chain 1, then chain Teemo to deal damage to it as Chain 2, making it a legal target for Gust before the chain resolves?

Ruling: No, this does not work. A unit must be a legal target at the time you play Gust. Damage does not reduce a unit's Might, so dealing damage would not make it a legal target anyway.

Sequence:

• If you want to use Gust on a high-Might unit, you must first play a card that reduces Might
• Wait for that Might reduction to resolve
• Then play Gust (the unit is now a legal target)
• This can be done as a reaction since you can react again after the Might reduction resolves

Nuances:

• Dealing damage to a unit does not change its Might value
• Targets must be legal at the time a card is played, not when effects resolve