Rage Stone

This expanse of black-veined crimson stone is infused with the psychic residue of pitched battles and brutal atrocities. A creature standing on a square of rage stone feels itself consumed with negative and violent emotions that it must unleash.

    Effect: A creature that starts its turn in a square of rage stone must make a melee attack on that turn or takes 5 psychic damage per tier.
    Usage: Creatures that are comfortable making melee attacks suffer few ill effects from rage stone, aside from lingering emotional turmoil that has no game effect. Creatures that prefer to stay away from melee combat (including most PC controllers, for example) are the most likely to take damage from rage stone. Putting rage stone at the periphery of an encounter area can play havoc with PC controllers and ranged strikers, as well as with artillery monsters.

Published in Dungeon Master's Guide 2, page(s) 61.