I found the easiest way to kill him was to grind my lich up to about 160 health/200 mp and then use the flame shield attack that he/she sometimes has the option of having. When you get down to the smallest of blobs it destroys them and the mages pretty much instantly
The teacher said we could be anything we wanted when we grow up. He wasnt talking to you son, now go out back and practice digging some holes.
Killed it with a Dragon. Being able to fly makes the earth spike enemies nothing but +6 HP back to me (was running 3 Vamp runes) and as for the boss I'd simply fly up to one corner so they all collected on the edge and then swooped to the other side and lit them up as they came across the screen.
Barbarian shout is useful to isolate a blob, and having the trait where spikes dont pop up helps a ton since the tiny ones usually stay on the bottom level. I killed 1 half first (left a big blob from first split for last) and always killed the mage before continuing on. Each blob took 4-5 hits so took awhile.