Here is the full list of all 28 SpellKnights achievements.
Reach 1000 successful hits
Reach level 10
Reach level 20
Reach level 30
Reach level 40
Reach level 50
Reach level 60
Reach level 70
Reach level 80
Reach level 90
Reach level 99
Win 5 games
Win 25 games
Win 100 games
Kill an enemy with a melee attack
Win a round without getting hit
Win a round with 1 hp left
Win a round using only fire
Win a round using only water
Win a round using only Earth
Win a round using only Wind
Stay 25 seconds inside a shield
Destroy 5 projectiles with their opposites elements
While having the Speed run power up, destroy three power ups
While having double damage power up, kill a player
Get hit while having shield creation power up and 1 hp left.
While having shield reflection power up, kill a player with the projectile reflect
Fall into the water