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