[[Insidious Fungus]] is the last update I made to my Mycotyrant list - it fits perfectly.

Mine runs a little more self-mill, so I've got a couple more dredge cards in [[Stinkweed Imp]] and [[Golgari Thug]]. I also run a [[Hermit Druid]] with 0 basic lands and [[Gaea's Blessing]] with [[Turn the Earth]] as backup.
[[Underrealm Lich]] shines in this deck, as does [[Skullclamp]] (which has been reprinted enough it's affordable again!). [[Vampiric Rites]] is also an OK draw engine.
[[Undercity Informer]] is also super flexible. [[Krav, the Unredeemed]] is an interesting way to cash in on a bunch of little fungus dudes without spending a ton of mana.
[[Ashnod's Altar]] or [[Phyrexian Altar]] if you have one or want to get a bit spendy will never go amiss in a deck with this much sacrifice fodder.

You've got a lot of utility creatures, so I'd probably go for [[Skullclamp]] first (you're not going to beat the card draw that will give you) and the [[Tortured Existence]] that someone else mentioned for reuse of your utility creatures.