This is a fine deck for Silverheart. You have some lower drops, which are all he needs to be functionally sound. I'd drop the Wurms and another fatty for them.
I would maybe add some sort of Fyndhorn Elves or Birds of Paradise as at least a 2-of to make sure you land your turn 1 mana dork, since your guys start at 3 mana really. Explore seems like a fine cut for them. They do so much more work than that card.
Prey Upon is the best option out of those, especially when you add Wolfir. If you add a 2-drop, Strangleroot Geist is awesome in general, but gets better with the fight mechanic
If you run post, you should add in Primeval Titan as well.
I would maybe add some sort of Fyndhorn Elves or Birds of Paradise as at least a 2-of to make sure you land your turn 1 mana dork, since your guys start at 3 mana really. Explore seems like a fine cut for them. They do so much more work than that card.
Prey Upon is the best option out of those, especially when you add Wolfir. If you add a 2-drop, Strangleroot Geist is awesome in general, but gets better with the fight mechanic