- Gravecrawler, Reassembling Skeleton, Bloodsoaked Champion and Nether Traitor. Basically any creature that brings itself back easily and repeatably. I think you want to do it for 2 mana or less, and these are the ones that fit this criterium. Are there any other cards like this that I've overlooked?
- Promise of Immortality brings back a creature and itself once per turn, generating two Tormod triggers each time. Fun times!
- Shirei, Shizo's Caretaker brings back small creatures every turn.
- Colfenor, the Last Yew is interesting because Tormod makes 2/2s, which can bring back creatures with 1 toughness through Colfenor, in turn generating more 2/2s.
- Tortured Existence triggers Tormod repeatably for one mana.
- Phyrexian Reclamation does the same for 2.
- Luminous Broodmoth, Mikaeus, the Unhallowed and Cauldron of Souls (as well as any Persist creature) can trigger Tormod at least once, but you need a way to remove the counters to do it more than once.
- Raven's Crime is a one mana retrace spell, turning every land into your hand into a Tormod trigger.
Have you found any more interesting engine pieces for Tormod? I'm looking forward to your ideas!