Id personally like literature/imagination materialization. The whole concept of powers not being controllable, manifesting beings more powerful than yourself really appeals to me.
For artifacts the H dial is my favorite. I love seeing different unique powers, outfits, etc. and always liked the idea of following the same person with different powers everytime they tried to use them.
My personal favorite power-granting artifact would be a Lantern Power Ring. Especially orange, cause Larfleeze is my boy. They are literally some of the most powerful objects in the known and unknown universe.
Favorite straight-up power? I’ve always been a huge fan of Spider-Man and Superman. But there’s also Wolverine with his godlike healing factor. There are too many cool powers to choose a favorite.
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There’s a reason there’s only one orange lantern you know