It is victreebel.
We are rivals,
We both have seprate arrivals,
When you see one of them, at the end it's flying,
when the other one battles, it certainly ain't dying!
One of them is around eight, while the other is around four,
When they meet, there is hurt galore!
While one has a black-yellow design,
The other one's a slim long feline.
Try that one!