Kirby.
His ability to inhale at a superhuman capacity and then copy the abilities of anyone he inhales/swallows giving him insane adaptability or produce a helper with the abilities of the inhaled enemy which effectively gives him a friendly version of the enemy or simply spit it back out as a flaming star. And there's the fact his lack of skeletal structure allows him to bypass many problems a normal body possesses (e.g. he can fly/glide due to how light he is and his inhalation ability).
And this is just one. A Universe's worth of Kirbies would be unstoppable.
His ability to inhale at a superhuman capacity and then copy the abilities of anyone he inhales/swallows giving him insane adaptability or produce a helper with the abilities of the inhaled enemy which effectively gives him a friendly version of the enemy or simply spit it back out as a flaming star. And there's the fact his lack of skeletal structure allows him to bypass many problems a normal body possesses (e.g. he can fly/glide due to how light he is and his inhalation ability).
And this is just one. A Universe's worth of Kirbies would be unstoppable.