Thanks to Scourge_lover156 for suggesting this. Mega serperior gets chlorophyll, doubling its speed in sunshine. After the boost its speed rests at 286, far outspeeding everything. Its speed, sp attack, and defensive stats rise. Its appearance changes to where its body grows leafy armor. Leafs cover its back and aid in photosynthesis. It also gets more golden coils around its body.
Stat boosts:
30 speed
40 sp attack
15 defense
15 sp defense