Fierce Stab- Even back in the days of yore when skill training was free, pretty much all the use this skill got was early mages using it to shank slimes. It could cost 0 SP (Regain SP while still getting to use 70 power attacks!) and I still don't think it would see any use. (But maybe, just maybe, we'd see mages with Tormentor and Bloodlust using sacrificial daggers to regain 15 SP in an attacking turn... eh? eh?)
Heavy Blow- As above, but for hitting Chindi in Tower 1 1/2 instead of slimes.
Feral Claw- As above, but for... uh... Shikigami? Okay, nobody used this except random-start characters with a Redcap and desperation.
Lucky Charm- Pre-currency pipedreams of rock-throwing brigades aside, ain't nobody got the currency to train their demons this, let alone themselves. Maybe if it was a free action with a cantrip cooldown we'd see some bizarre buffing Wizard/Lucky Charm/Lob Stone shenanigans. (But I doubt it.)
Throw Rock- No Ferret, nobody trains Artemis (or anyone else) to throw rocks to squeeze in a few more tactical 70-power hits. NOBODY. They just teach someone else Refresh, or teach Artemis Tireless, and/or Tormentor, and/or Vigorous, or even WARMTH because they pair her with an Ukobach but not Throw Rock.
Agility- Agility is not a skill but my attempts at going FULL AGILITY have been pretty mediocre. But by golly I'm going to keep doing it until I win that Riposte build.
Exhausting Bite/Desiccation/Frostbite- the SP of the enemy is usually irrelevant compared to their HP due to the shortness of fights, but if it's very important to shut them down, you should probably just Infect them, because that will, in addition to slowing down that pesky +5SP per turn, prevent them from healing effectively and possibly open them up to a bunch of Infection shenanigans. I suppose there could potentially be ice shenanigans too with stuff like a Ice-party with AoE and Winterkill and Wizard really ripping up the enemy SP right quick, but see earlier notes on Lucky Charm, Throw Rock, and pipedreams.
Corrupt- Isn't it weird that we find this AFTER Vile Dance? I think that's weird.
Uncurse- Yeah, all the foo-down are bad, but you sort of just have to suck them up because if your Uncurser and the enemy Curser blow all their mana fighting over curses, the real net effect is that you don't have any healing (or frontliners, or support, or whoever the heck you taught Uncurse to.) Plus it only shows up late, and it's only Manabananapranahosannagals who have the nasty Slow by then anyway. Calm>Cleanse>Absolution>Uncurse, that's the truth, yessirreebob.
Healing Rain- Some stay dry while others feel the pain healing raaaaain