Crusher Tentacles are spawned during the Yogg-Saron encounter at the end of the Ulduar instance.
Attacks and abilities
Erupt - A tentacle bursts from the ground, dealing 1488 to 2012 physical damage to enemies in a small area and knocking them back.
Diminish Power - Weakens enemy units in a large area around the caster (50,000 yards), reducing the damage they do by 20%. Channeled. Stacks up to 4 times. Being hit by a melee ability will disrupt this cast.
Focused Anger - Enrages the caster when hit by attacks and spells, increasing attack speed and damage dealt. Stacks up to 99 times. Damage dealt is increased by 3% and attack speed is increased by 3%. Lasts 1 second. Refreshes upon being hit.
Patch 3.2.0 (04-Aug-2009): Crusher Tentacles in the Yogg-Saron encounter spawn a little slower in 25-player mode allowing a bit more time for players to clear out the Illusion room.
Hotfix (2009-07-02): "We've made one additional change to a specific element of the Yogg-Saron fight. Since the fight went live, there has been a hidden protection for players that prevents the casting of Psychosis and Malady of the Mind on targets with less than 30 Sanity. However, because Malady of the Mind has a slow missile speed and the hidden protection could take a second or two to apply, it was quite possible for the 30 sanity targeting threshold to be breached by these two random unavoidable effects. To try to address this we're raising the threshold to 40 sanity, and increasing the missile speed of Malady of the Mind. Note that the spells are still being cast just as often, so the net sanity loss to the raid will still be the same. This hotfix just evens out the random targeting of the spells across the raid. Also note that the threshold is for targeting purposes of those two spells only, and this fix means Psychosis or Malady of the Mind can still bring you below 40 sanity. If you have 41 sanity, you're a valid target and can then be brought to 32 sanity by a casting of Psychosis on you."
Hotfix (2009-06-15): "Focus Anger, on Yogg-Saron's Crusher tentacles, will no longer result from pet attacks."
Hotfix (2009-05-14): "In the Yogg Saron encounter, Paladin Judgement spells will no longer cause Diminish Power from Crusher Tentacles to cease channeling."