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