ToME WikiKhymChanur: 3.0.0 has symbiant monsters (moving "m"s), but only three different types so: symbiant adept, smybiant and ancient symbiant. The symbiant adept can hit and blow poison spores at you, the symbiant can additionally blow fear spores at you, blink self, and summon kin, and the ancient symbiant can additionally teleport self and summon monsters. I think it'd be neat of the symbiant monsters varied based on what exactly they were in symbiosis with. So a "green mold wearing symbiant" would do emit fear spores, a "hairy mold wearing symbiant" would emit poison spores, a "Quylthulg wearing symbiant" would blink self and summon monsters but not emit spores, and so on. Their level, HP, AC, speed and such would vary based on what symbiont they're wearing.
It'd also be cool if the symbiont added their attacks when the symbiant hits, like for symbiant players, so that the mold they're wearing would only spray spores on you if the symbiant itself hit.
NerdanelVampire: I wonder if the symbiants could be done as a monster ego that switches off the NEVER_MOVE flag among other things.
KhymChanur: Huh, that's an interesting idea.
NeilStevens: It'd be neat if we could actually generate a symbiote in the way we'd generate a summoned never-moving pet, and give the symbiant the appropriate spells and attack effects at the time of monster generation.
You are already elbow-deep in embedded things in flags, after all, heh.
KhymChanur: Oh, I wasn't suggesting that the symbiant monsters actually have a symbiont, just that they'd act like they did. My thought was that there'd be a different race entry for each type of "FOO wearing symbiant", with the appropraite spells and damage types coded by hand.
DarkGod: well there is a monster generation hook, we could use it to actually create a new monster to use as a symbiote. Then make a monster spell "use symbiote powers" and a new monster attack "use symbiote attacks", not even too hard I think 
NeilStevens: I feel like a whiny user here, but I do think that it'd bloat the monster list too much to take the symbiants and multiply them by the number of possible symbiotes. At their native depth the dungeon would be *crawling* with them!
RavenRed: As an ego-type then? That't bloat the egos.lua file a little, but would save a little in the monster files. BTW, can we FORCE egos onto monsters as a default?
ElvishPillager: Hmm, why not have it be an ego of the symbiote, rather than the symbiant? Thus, you would have "Quylthulg" -> "Symbiant wearing Quylthulg" where "Symbiant wearing " is the ego name; the ego does little more than remove NEVER_MOVE and recalculate move-speed, and there would be no actual "symbiant" monster.