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.
Avoid the Dealy Dangler Fish.
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.
Eat 25 Lizards.
Drink 25 Steins of Mead
Defeat an enemy by setting them on fire.
Obtain all the Runes of Health
Kill 25 Enemies.
Kill 100 enemies.
Kill 250 enemies.
Kill 25 enemies while Berzerk.
Kill 100 enemies while Berzerk.
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.