Brutal Legend Mission 20: Abomination Overdrive (FINAL MISSION)
Flanking Doviulus' main area are two large pillars with eyes. You must summon your army to attack the base of these pillars to weaken them. Don't attack both at the same time; pick one and muster all your attacks towards it until it is weak and turns it's "eye" towards the crimson hallways on the far left or far right of the level.
Summon the Deuce, drive it up through the hallway, and then hit your nitro to make the jump into the eye, destroying the pillar. Now all you have to do is the same thing to the other pillar while defending your merch booths from enemies.
Once the second tower is destroyed, drive the Deuce straight through into Doviculus' lair for the final battle.
Doviculus has a pretty standard pattern that is easy to figure out: attack him, he retreats to the chains, and then calls on his minions to try and kill you. What makes this entire battle easy are your Solos, particularly Bring it on Home and Facemelter, both of which will damage Doviculus and any nearby minions he has summoned to the battle.
The way to get Doviculus off of the chains is to use Clementine's lightning attack to break the chains one at a time. Once all of the chains are broken, Doviculus will meet you on the ground for a short period of time.
Continue this pattern of Solos and good combo attacks against him until he is finally defeated, finishing the game.