Mario Versus Metroid
Samus' antics amongst the space pirates rips a hole in quantum reality. A lone metroid passes through the hole before it closes. In one of a myriad of realities, Mario missed a jump and is falling to his doom when the hole appears and he falls through it, winding up in a flat plain. The only other living thing he can see is the metroid, which immediately goes on the attack. Mario manages to avoid its initial charge, and activates the only power-up he has with him at the time: an Ice Flower.
Can the Frozen Flinger of Frost take down the second greatest hunter in the universe, or will the metroid have Italian for lunch?