Eating 2 devil fruits will make most people explode like a bomb. There's a very slim chance of surviving, but if u do survive even though u consumed 2 devil fruits, your power would be very strong yet unstable. The only character in One Piece to have gotten 2 devil fruit powers and survived (also he's very strong) is Marshall D. Teach. He has the powers of the Yami Yami no Mi and Gura Gura no mi. Source:
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