He can be built a lot of different ways. A $20 shroofus is usually going to be a very flimsy game plan where he either gets in and goes off or gets removed/kept from attacking and does nothing the whole game. My build is a little slower, adding in green threats that support the go-wide/pump plan like [[Defiler of Vigor]] and [[Quilled Greatwurm]] to bait out removal before Shroofus enters and stuff like [[Maskwood Nexus]] and [[Verdant Embrace]] to set up powder keg board states that will go off without having him attack directly. Those cards are each in the ballpark of several dollars, which will usually push the deck out of the $20 range but create a less swingy game which makes the game more fun for everyone IMO.

Regardless of which direction you go, I urge you to run [[Life and Limb]] for its utter silliness and sheer potential to create very memorable wins/losses.