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