Worldspine Wurm on turn 4? Okay. Here's how the deck works. Get Boneyard Wurm out (if you don't have a creature card in your graveyard then play wildguess or faithless lootings). Play Descendant's Path. Get Beast Tracker to put the Wurm on top of your deck. Play it without paying mana cost.

Your opponent wants to play removal on your wurm? Thanks man, get 3 tokens and goes back into deck. Get wurm in your opening hand? Play Faithless lootings or Wild Guess to discard him (thus putting him back into your library)