Who knew Lorwyn had such an extensive education system?
First strike is powerful, m'kay? It gives all of your under-tough creatures a great chance to survive combat. Giving all of your red creatures first strike is really powerful. This little guy also comes out really early and is a goblin to boot. Too bad he's so tiny.
Pros: Costs 2, gives red first strike
Wither is powerful, m'kay? It really leaves a lasting impression on the board even after the creature with it dies, either in the form of life loss or weakened creatures. Giving all of your black creatures wither is really powerful. It comes out early game since it only costs 3 (drop it on turn one with a Dark Ritual perhaps?). This thing's also on a pretty beefy body (at least toughness-wise), so it's a really good card.
Pros: Gives black wither
Cons: Only 1 power
Unblockable is powerful, m'kay? It means, well, your stuff can't be blocked. Giving all of your blue creatures unblockable is really powerful. However, this guy costs 6, which means he won't be around until the late game, and by then you might already be dead. Great in EDH though.
Pros: Gives blue unblockable
Cons: High cost
Tapping to gain a life is really weak, m'kay? It doesn't really do much in the long term. Giving all of your white creatures "tap to gain a life" is really underwhelming. I guess you could block with creatures then tap them (that's tech right there). This mentor also costs 5, so it's underwhelming in the late game.
Pros: Gives white the potential for lifegain
Cons: Little lifegain, causes creatures to tap, costs 5
Trample is powerful, m'kay? It makes chump blocking pointless since you'll be taking damage anyway. Giving all of your green creatures trample is really powerful. It does cost 6, but since it's in green, that's turn 3 or 4. It also has the biggest body of all the mentors, which is great.
Pros: 5/4, gives green trample
Cons: Costs 6