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