Generally, you should include:
What went wrong? Started fight with Idol of Ruin in Corrupted Lake as a Lich using Mouse n Keyboard (not WASD). Tried channeling Drain Life and mousing over the Idol of Ruin. Drain Life never targeted the Idol of Ruin. Dragged mouse around randomly while channeling Drain Life, never hit Idol of Ruin. Spirit Plague, Aura of Decay, and Golem were all able to hit Idol of Ruin.
Log File
Screenshots (via a site like imgur) or video, if applicable
Thanks!