Here is the full list of all 27 Cosmic Magus achievements.
Play your first match.
Kill 50 enemies in one match.
Kill 100 enemies in one match.
Kill 200 enemies in one match.
Survive for 180 seconds.
Survive for 300 seconds.
Kill 70 enemies with frost spells in one match.
Kill 70 enemies with arcane spells in one match.
Kill 70 enemies with solar spells in one match.
Reflect 30 projectiles with the solar reflect spell.
Steal 300 spells in one match.
Kill 5 enemies with one frostbite cast.
Destroy 8 enemy abilities with one Impale.
Blink 45 times in one match.
Use 10 Arcane Bolts within 1.5 seconds from one another.
Kill 5 enemies with a single Piano.
Kill 4 solar warlocks with one slash.
Reach a score of 100 on the map Stairs to Valhalla.
Reach a score of 100 on the map Cubic Prism.
Reach a score of 100 on the map Rainbow Bridge.
Reach a score of 100 on the map Wizard Tower.
Kill 6 enemies with one icicle.
Reach a score of 100 on the map Lost Woods.
Slow enemies for a total of 60 seconds in one match with brambles.
Kill 5 enemies with one boomerang.
Morph 30 times in one match.
Kill 10 enemies with a single lava pit.