Probably my biggest request for mutations would be an on-off screen similar to the Bionics interface. Some stuff really feels like it ought to have a switch installed: Insect Wings, for example.
Mod to existing mutations:
Tentacles permitted to Grab (on a crit?) and possibly Throw as well as the existing-but-pathetically-weak Slap.
Leg Tentacles seem like they shouldn’t allow footgear. Where are you wearing it???
New mutations:
Fangs->Saber Teeth: You have a pair of 8-inch fangs. They slow your eating and make wearing mouthgear impossible, but allow a devastating bite attack. (Yeah, this should be a net minus)
Claws->Large Claws: More damage, hand encumbrance 2, no gloves. (I’m assuming the current Claws are retractible.)
Large Claws->Tearing Claws: Your claws remind you of that old dinosaur movie, and go through flesh like butter. Can one-shot most Zs but no gloves, hand encumbrance 4. (Thinking raptor claws here.)
Large Claws->Ripping Claws: Your hands have become extremely craggy and muscled, at the expense of precision. No damage increase over Large Claws…but can burn nutrition/incur Pain to rip through concrete, rock, etc. No gloves, hand encumbrance 5 so no guns either.
Haemovore: Your mutation-based attacks can draw blood, doing additional damage and providing marginal nutrition.
Leaves->Photosynthetic: Sleeping outside, on diggable terrain, during daylight causes you to lightly take root. You gain the effects of Inconspicuous & Heavy Sleeper whilst asleep, but gain Nutrition at a good rate as you process nutrients from the soil.
Bat Wings->Large Bat Wings: They still don’t help your balance any but they make for an excellent glider. Can choose where to land when jumping down a Z-level, with bonus to the Dodge roll. (As seen in Batman Returns.)
Web Weaver->Web Spinner: You’ve finally gained control over your silk glands. Press [key] to lay webbing; takes X amount ot movement points.
Whiskers->Long Whiskers: You can feel air currents sufficiently to help you navigate in the dark. Mouthgear can fit but is irritating: 1 Pain permanently so long as you wear it. (Can locate walls/doors in range 5 without light. As seen in cats.)
I think that’s enough for now.