Armityle the Chaos Phantom Cannot Attack And it isn't gain 10000 ATK Points After It Summoned
The anime version only gains 10,000 attack when battling another monster. Also, if you summoned him using Time Fusion he cannot attack the turn he is summoned.

An actual Bug I noticed with anime Armityle is his effect to be switched to the opponents side of the field. When his effect then forces him to return to your side of the field your other monsters are destroyed, although the only ones that should be are the opponents.