Gift of Immortality is the source of many a repeatable combo, and Squee, the Immortal is even harder to get rid of than Reassembling Skeleton

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Usually, big dump mana, make token cards focus primarily on that, but should the Commander make it around the table again to lead his charges into battle, thats additional damage and evasion even for decks that dont use typal strategies
The only downside is that if/when your mana dork gets removed, you also stand to lose your biggest attacker