>>37529059Oh right, I forgot about that.
>Although, weirdly, if Moltres uses Burn Up and then Roost, it becomes typeless instead of Normal.This one's pretty simple: Moltres is still internally Fire/Flying, so it doesn't trigger the pure-Flying special case.
Type changes presumably go over the original type instead of replacing it, since that way you can't accidentally make them permanent.
>>37529076Why would you need STAB on Roost? It does no damage.