I like Mulch too, and have been playing a deck that looks something like this in Multiplayer/Casual for a while now:

G/b Mulch

4 Sakura-Tribe Elder
4 Eternal Witness
2 Gurzigost

4 Mulch
4 Gaea's Touch
4 Skullclamp
4 Beacon of Creation
4 Grizzly Fate
1 Crush of Wurms
1 Coat of Arms

4 Death Match

21 Forest
3 Swamp

1. Mulch dumps Grizzly Fates + Crush of Wurms into the graveyard and contributes to threshold.

2. Gaea's Touch is a remnant from an older version of the deck with Waiting in the Weeds, but it obviously works well with Mulch and Beacon.  Plus, they go for something like 10 cents versus $10 for Explorations.

3. Death Match is insane with Beacon and Grizzly Fate.  Ditto Coat of Arms.

It's been fun to play, you know, if you like attacking with creatures, although it REALLY depends on Mulch to get going and has approximately zero tricks.

Some other fun stuff/ideas:

Randy Buehler + Mulch
1998 US National Championships- Standard Constructed (5-1)

2 Archangel

1 Aura of Silence
2 Cataclysm
2 Creeping Mold
2 Disenchant
2 Enlightened Tutor
4 Gaea's Blessing
3 Gerrard's Wisdom
4 Mulch
4 Oath of Druids
4 Scroll Rack
4 Wrath of God

4 Brushland
7 Forest
4 Grassland
7 Plains
2 Quicksand
2 Wasteland

Sideboard:
4 Abeyance
2 Armageddon
1 Choke
1 Circle of Protection: Red
2 Disenchant
1 Elephant Grass
1 Emerald Charm
1 Gerrard's Wisdom
2 Jester's Cap


Zvi (!) + Mulch
http://www.classicdojo.org/d981/dks.980324zmo.txt

-cheers, cm

A few thoughts:

Have you had any problems getting the first green mana?  I'm thinking that Wirewood Guardian might be worth it in the Tusker slot for this reason.  Or maybe some combination of the two.

I can't believe I'm about to say this but Titanic Bulvox might be good here.  In the Crash of Rhinos slot.  You lose one point of power for the ability to play it as a morph.  The morph cost is a little tricky though at 4GGG.

As for Trike substitutes, Savage Twister, Elephant Grass, or Slice and Dice come to mind, although none of them can double as a win condition like Triskelion, and Slice and Dice is probably too difficult to cast.  Or what about Ancient Hydra or Squallmonger? 

I might try the Twister and swap the Rhinos for Rootbreaker Wurms, since they're a bit cheaper and tougher.

I don't know if it's worth wasting an uncommon slot on, but Sensei's Divining Top might be halfway decent given the amount of shuffle effects you have and the lack of card drawing/sifting/filtering/etc..  Fierce Empath might also be a decent way to tutor up a win condition.

Hope that helps!

-cheers, cm