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Some good candidates for the effect are cheap characters like Owl, Logical Lecturer or Lefou, Bumbler who you won't mind getting banished in a counterattack, but anything you can use to take out your opponents' characters works well with The Queen
38/132 Erika's Bellsprout
4 Emrakul, the World Anew Foil Etched - $84.42 The nice thing about Emrakul, the World Anew is that the designers behind this set managed to keep Emrakuls devastating power, while still making it feel mechanically unique
So if you want to see what direction to upgrade ol' Nivvy, their list is a great place to start
If a creature has Menace and gains an ability that makes it unblockable, then it cant be blocked