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