Facing Dat mage you are likely to encounter:
EASY/COMMONLYEFFECTIVE
Ignite, The very bursty 3 second stunner with a short CD.
Frostbite, The ice snare that roots you for a solid 6 seconds with a soft CD
Erupt, The volcano that slams heavy dps then dots the area for more owe. A slower CD
Miasma, The teleport that will quick stun and boost the mage dps long enough to slam out a chain of rippage. Slower CD
MORE EASY//NOTALWAYSEFFECTIVEANDNOTALWAYSAFACTOR
Redemption, Plasma shield, Righteous defense. When the mage wants to take a large mana hit rather than HP, and wants to reduce incoming damage by a sizable/great amount. Very easily wasted if inexperienced however.
Cauterize, The big instant heal for ~5K HP on a slow CD.
MEDIUM/EFFECTIVE
Despair, The moderate 3 sec silence that can reach deeper than a unit-targetted attack. A slower CD
Frostbite with extra talents, The quick and large boost to footy speed upon dropping frostbite.
HARD/NOTSUREATALL
Repent, When the mage feels a little bit noped and wants to mirror 25% of your dmg dealt to him back onto you. Long CD.
Dragon Breath, When the mage knows you're gonna silence him he drops a wicked frostbite dragon breath combo for maximum glory in battle.
NOTE: THEORY IS AN ASS ITCH I HAVEN'T EVEN SPECED INTO PVP HP.