Why does Mega Aerodactyl sometimes take regular damage from super effective attacks?

Question

When I used mega Aerodactyl in the battle tree, The opponent Wailren used frost breath, and the 1st 2 times it did normal damage, the 3rd time it was super effective and he fainted. How is that possible?!

Comments

@Cobruks - Rock types aren't weak to Ice type moves. Could the fact of Aerodactyl being weak to Ice type moves help?

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@Azelfeo - Ok i looked at the type chart: Rock 2x against Ice Flying 2x weak against ice. Ok since Aerodactyl is a rock/flying type, ice should just be 1x effective right?

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@Cubruks - It would be 2x effective.

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ok then! I think i could write a good anwser for this Question. Thanks for helping me, all of you. Me and Luxray thank you.

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But since the Flying type was removed when using Roost, Frost Breath should be 1x effective

Answer 1

Mega Aerodactyl has a x2 weakness against ice type moves. When the move roost is used, the flying type is taken away for the remainder of the turn, losing the weakness against ice for the remainder of the turn.