A tricky enemy encountered during the Unintended Consequences quest.
Strategy
At the beginning of the fight, the Whim will spawn 4 images of himself, of Normal rank. If your party can hold the various targets, this is a relatively straight forward battle. Send your main tank on the original Trickster, a second tank to hold a couple of the copies, and let the rest of the party burn or avoid the remaining copies. As the DPS and/or off-tank burn the copies, redirect some of their damage to the main trickster.