Victreebel is another dangerous special wallbreaker in the tier. High special attack, high base power STAB in Leaf Storm, Strength Sap to heal itself, Sleep Powder to punish switchins. There isn't much that switches into Victreebel well at all and it's hard to say which set it's going to be. Will it have Sleep Powder? Sunny Day with Weather Ball to outrun the whole tier? Physical SD? It's versatility makes it a high tier pokemon in PU.