Here is the full list of all 29 Rune Classic achievements.
Drink 25 Steins of Mead
Obtain all the Runes of Health
Get beheaded in multiplayer.
Get "First Blood" 10 times
Kill 100 enemies while Berzerk.
Behead 100 opponents in multiplayer.
Defeat an enemy by setting them on fire.
Kill 100 opponents in multiplayer.
Kill 50 opponents in multiplayer.
Behead 25 opponents in multiplayer
Behead 10 opponents in multiplayer.
Beat an opponent to death with a severed limb.
Get a 10 player kill spree in multiplayer.
Kill 10 opponents in multiplayer.
Complete the game (any difficulty).
Complete the game on Medium difficulty.
Complete the game on Hard difficulty.
Defeat Sark Conrack.
Kill 25 enemies while Berzerk.
Become Sark Ragnar.
Get all the weapons in the game.
Defeat the Trial Pit Beast.
Defeat the Dark Dwarf.
Make your way through Hel's Chamber
Kill 250 enemies.
Eat 25 Lizards.
Kill 100 enemies.
Avoid the Dealy Dangler Fish.
Kill 25 Enemies.