The Wall of Bone is said to be an aspect of the Great Wall in Hel, where the bones of all sinners wait for Ragnarok, when Hela will call them forth for the final battle.

Wall of Bone

Defender (This creature can't attack.)
{B}: Regenerate this creature. (The next time this creature would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)

30th Anniversary Edition

"Graveyards are sacrilege! A waste of perfectly good bones."
—Keren-Dur, necromancer lord

Duel Decks Anthology: Garruk vs. Liliana

Duel Decks: Garruk vs. Liliana

Magic 2010

Defender (This creature can't attack.)
{B}: Regenerate Wall of Bone. (The next time this creature would be destroyed this turn, it isn't. Instead tap it, remove all damage from it, and remove it from combat.)