Frost:
An unbreakable stun that they can easily 100-0 any class with a 1000+ resilience.
CounterSpell on a very short cool-down and does not need to have a certain pet out to use and the target doesn't even need to be casting to be silenced. Imp Counterspell is in the FIRST tier of Arcane for fucks sake. Good luck being a Demo Lock and popping Metamorphosis, with a mage anywhere in visual range, your 3 minute cool-down will be rendered useless by a 15 second cool-down.
Spellsteal: Good luck being a paladin with a mage anywhere in visual range. Your 3 minute cool-down will be rendered useless by a 15 second cool-down.
A 15 second cool-down Blink that can get them out of stuns and roots and is the single best ability in all of PVP. And Blink doesn't need a teleporter to be put down with a 40 yd range. (And the lock teleporter has an even longer cooldown than Blink.)
10K Ice Lances on 1000+ resilience. Thats Ice Lance: no cooldown, instant cast, trivial mana cost.
Frost Nova that can be applied twice in a row.
Frost Armor that applies a snare even to ranged attackers, even a Paladin can be snared when Judging a Frost mage from range.
2 different shields that can be applied one after the other, and Mana shield burns hardly any mana.
Ice Barrier applies Frost Nova because of Shattered Barrier when it breaks, even to ranged attackers.
Reactive Barrier, (shit like this makes me laugh, free auto Ice Barrier when taken below 50% health, so pro you dont even need to use a GCD to provide a free shield that will Frost Nova anyone who breaks it)
A pet (why the fuck anyone thought they need a pet is beyond me)
Invisibility
Icy Veins
Ice Block
Cold Snap: reset all your cooldowns, because good players need to be able to pop all their cooldowns twice in a row.
Mirror Image: causes attackers to drop target, (wtf???) and yet another DPS cooldown
Ring of Frost: will freeze anyone who crosses into or out of the ring, it will freeze multiple times also, so if you trinket the first and touch the ring again you get frozen again.
Frostfire Orb: God forbid mages not fully benefit 100% from every single new spell unlike other classes.
Fire:
Faceroll DPS and casting Scorch while moving.