Special Summon them, but their effects are negated
Achilles' Heel: Downplayed, Leo specialises in using allies, with his signature ally letting him put down more at once, so any game effect that targets them and cause them to be defeated/discarded can disrupt him, but he still has a decent cardpool and base stats to still be effective without them
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As could be inferred by the name, the Nine-Lives Familiar card is a cat creature that has an effect that starts upon casting
Black can play a bunch of synergistic artifacts, and MDFCs like Malakir Rebirth to boot
This allows you to cast any instant speed mill effects in response to Thassas Oracles trigger, forcing your opponent to counter it, or for you to win the game