“Conjure waves of abyssal flame to immolate enemies held paralyzed in your spiteful grip. Feast upon the carnage of battle, gaining strength as foes perish around you, their attacks diminished by your very presence,” the Dark Rift update page says. “Tear a rift in reality to teleport yourself and your teammates across the map, delivering bloody retribution to any who would defy the will of Vrogros the Underlord.”
I guess that's one way to put it. Described a bit more prosaically, the Underlord's abilities include Firestorm, an area-of-effect fire spell; Pit of Malice, which traps and damages enemy units; Atrophy Aura, which weakens nearby enemies and grants bonus damage to the Underlord; and his ultimate, Dark Rift, a teleport that carries the Underlord and all nearby friendly heroes to a selected friendly unit's position.
The update also brings a new post-game summary to Dota 2 that will provide “detailed reports on different aspects of player and team performance that will help break down game flow and visualize critical turning points.” Scoreboards, graphs, teammate stats, and other relevant information will all be at your fingertips—and because statistics aren't much good if they can't be viewed over time, summaries of past matches will be saved for later viewing.