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