Pretty standard stuff. The main goal of this deck was to be mono-colored creature deck, with good flexibility and resistance to decks that can give creature decks trouble. Spirit Loop ended up finding its way in because I like the durability of the card and a few birds of paradise seemed like an easy solution to working it in. Spirit Loop also seems like the best choice to stick on Endless Wurm (Rancor should go on everything else without trample).

The basic strategy is to get on the offensive as soon as possible. Once Genesis is dead and in your graveyard (do this as soon as possible), you should be able to go willy-nilly with anything that has trample. After Genesis is dead, killing off your Eternal Witnesses and then bringing them back into play will let you bring back any non-creature card such as Overrun or Naturalize (although you can use them to bring back a creature too if you want).

Genesis and Eternal Witness seemed like solid choices to ensure you never run out of creatures to throw at your opponent. Naturalize felt mandatory, but is intended more to target enchantments. Artifacts should be taken care of with Molder Slug. The Ferrets will screw with your opponent's defense and the Mongrels will give you options if your opponent gets cheeky with protection from green spells/abilities. The Thornweald Archers will kill anything they hit but should be held back for defense if your opponent has a lot of fliers.

Sideboard is just random stuff I stuck over there. Haven't decided what to do with it, if anything at all.

Honestly, I can't think of anyway to improve this deck without changing its general concept. Any constructive input is welcome! Please be kind; I'm not a tourney player and haven't played Magic in awhile (just getting reintroduced, actually).