What would it be?
Personally, I'd have the power of Sorcery...does that even count lel. If not then telekinesis ;)
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The ability to control probability. What the probability someone will drop $1m in front of me? 0.0000000000001%? Ya let's crank that up to 100%. What's the probability I also have the ability to fly? 100%. Telekinesis? Bam! 100%.