Tag 667, closely related to tag 666, is used on Doom II's MAP07 in conjunction with the Arachnotron. This is the relevant code (from p_enemy.c, lines 1722-1727 in the Doom source code release): if (mo->type == MT_BABY) { junk.tag = 667; EV_DoFloor(&junk,raiseToTexture); return; } When the last Arachnotron dies, any sectors tagged with the number 667 are raised up by the height of the first sidedef's lower texture. If the first sidedef does not have a lower texture, the second sidedef is used.