I always wanted to make a fungus deck, especially one with Thallids, and Thelon of Havenwood makes a perfect commander for it. Thelon and his band of mycologists where set on making a source of food when they created thallids, a fungal species that made saprolings, a new source of food. The thallids gained sentience however, on over ran havenwood within days. This time the plane shifted Thelon is back, and hes collected his thallids to wreak havoc on the commander battlefields.

With the new commander ruling Thelon's color identity is actually green and black, despite him costing two green. This gives us access to some sweet removal in Maelstrom Pulse, Putrefy and the ever so cool Deathspore Thallid. It's advisable to let spore counters build up on your thallids, and only create saprolings when you need them, or remove them all when the thallid dies for a burst of saprolings!

This deck is a very aggro deck, winning either with a swarm of saprolings, or a big thallid beat down.

Life and Limb + Sporemound combo to make infinite saproling/forests! just make sure you have a way to stop it, like Alter's Reap

Attrition + Life and Limb + Urborg, Tomb of Yawgmoth another life and limb combo, but have all three of these on the battlefield and you can tap and sac a saproling to blow up a creature, not bad.

Savra, Queen of the Golgari gives us 2 life everytime we sac a saproling, which adds up quick

Doubling Season is just gross, doubling the number of spore counters and saprolings we make. left unchecked this and a couple thallids is easily a wincon.