Avaleur de ferraille cuirassé

Armored Scrapgorger's last ability triggers whenever it becomes tapped for any reason, not just due to its mana ability.

If the card chosen as the target of the last ability is an illegal target as the ability tries to resolve, most likely because it left the graveyard some other way, the ability will fail to resolve and none of its effects will happen. Armored Scrapgorger won't get an oil counter.