Not particularly dangerous by itself, but comes paired with 3 Mana Feeders whose arcane damage on the raid will be dramatically increased on players who received the debuff. It is possible to quickly dispel their debuff - but an easier tactic is to have someone (doesn't have to be a tank) range-pull the Mana Feeders and let the tank charge the Chaotic Sentience immediately afterwards, tanking it at a good distance away from the raid, out of debuffing range to those who deal with the Feeders. It's immune to Banish and stuns.