Steal would not work, because if you were standing next to someone, it may randomly change items with them which would be a pain in the ass.
Hover sounds like a cool idea that was kinda mentioned above ^.
Shift is a toned down version of blink.
Transportation is a lot like shift.
Temporal Mastery does not make much sense.
Fissure could be too easily exploited and would cause lag.
Shell is like a skill that is passive for dragoons (cant remember the name)
Pillars would be too easily exploited.
Encase could be exploited and sounds too OP
Crush would be hard to pull off and would be exploited
Bite sounds like a good idea.
Transfusion doesn't make much sense at all, it would basically be an attack.
Bloodlust sounds like a good idea
Armor Breaking Skill is waaay too op and would cause much more problems then it would resolve
assault is pretty much a skill dragoons have
Break/disable sounds like many other existing skills
block sounds like a good idea, but would not fit well as a skill
Counter sounds familiar, but I cannot remember what from..
Lightning Reflexes sounds like a good passive skill
Dupe and Clone would be horribly laggy and be way to op
Dark is not that useful, as it would be hard to make the place black for one person, and people can still see at night
Blind would be hard to pull off
Flashfire seems very unnecessary and useless
freefall would cause lag, may be exploited, and is pretty much doing damage for an increased amount of mana
Minds eye if passive would be alright, but for a mana cost, it would be useless as the other illusion skills would consume a large amount of mana too
Some of your criticisms are a little unjustified, like to say something is OP when it has no values assigned to it is just silly.
Being overpowered is relative to the rest of the damage output, effects, costs, cooldowns and durations of the rest of the spells and skills game. Since all of those aspects can be adjusted, there is no reason to say a non-existent skill is "OP" and it is also safe to disregard any of your concerns about mana cost.
All of these skills, except "Temporal Mastery" and maybe "Minds Eye" are meant to be activated, as such they all would have cooldowns, durations and conditions when they would be active.
Steal - would be activated like any other skill, I've seen it in minecraft already, it shouldnt be hard to implement effectively. There is no worry about randomly stealing from random people.
Shift - IS blink, to a degree. TRANSPOSITION =/= to Shift since with shift you're not trading places with anything, nor are you specifying a target.
Temporal Mastery - simply applies damage to certain teleportation spells, like Transposition.
Encase - wouldnt be OP, since all you would need is a pickaxe, if that, to break free. Its more for the crowd control effect than anything. As are the majority of the "Earth Spells"
Transfusion - simply says you pay (x) amount of life to receive (y times x) amount back, I'm not entirely sure whats so difficult to understand about that. You spend 10 hp and you gain a (multiplier x 10) back. If you dont have enough health to cast the spell, you can't gain that amount of life. So no, its not "just an attack"
Dupe - would produce no more lag than a summon or spawn would. Also whats op about a clone that dies in a couple of hits?
Flashfire - if you make your enemy believe they are on fire, they may retreat, or try to put themselves out, giving you time to do whatever you like.
I do agree some skills MAY be exploitable but, these are just ideas and none of them have actually been designed yet so its tough to say that they would be any trouble at all, other than programming the actions and visual effects in game.
