Giving your opponents access to an extra 2-4 mana during their second main phase can definitely be problematic if your opponent is holding a powerful card or two, but in exchange, you can snag 4-6 each turn, as no mana is given out when you lose life
Another incarnation of Gandalf makes the cut here, as does his former ally, the power-hungry Saruman the White
Under the current rules (as of writing this blog post) both of them would simply die as a state-based action due to the planeswalker uniqueness rule, so nothing special happens
Some, like Crackling Cyclops, grow stronger with each noncreature spell you cast, while others, like Balmor, Battlemage Captain, buff every creature you control
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