Quest One

Speak to any Wizard or Above in the Mages Guild if you're a Warlock or if you are Level 20 with a Reputation of 25.

Speak with Gavin Vette in Ald'ruhn and accept his quest.

Head to Odaishah.

Crescius is really fast, but he has a massive weakness to fire you can exploit.

Return to Gavin Vette.

Quest Two

Wait two to three days.

Return to Gavin Vette.

Head to the Suran Tradehouse and speak to Jastia.

Head to Bal Ur.

Nathyss is just inside the shrine, so you don't have to go far in. Nathyss has powerful poison AOE darts. He is resistant to frost, fire, and poison, but he has a severe weakness to shock and normal weapons. Use resist poison and dodge, shock the bastard, or equip your lowest-tier weapon and go to town.

Return to Jastia.

Return to Gavin Vette.

Quest Three

Wait two to three days.

Head to Molag Mar Redoran Stronghold.

Talk to Elvas Savel.

Head to Savel Ancestral Tomb and bring an intervention scroll. The easiest way through the tomb is to ignore all the enemies and just make a run for it.

Bolor Savel has a big shield spell protecting him, but he has a very bad weakness to magic.

Return to Gavin Vette.

Quest Four

Head to Maren Ancestral Tomb and kill Crazy Batou who is untouched by the mod.

Return to Gavin Vette.

Quest Five

Wait two to three days.

Return to Gavin Vette.

Head to Esutanamus.

Crescius is back. Remember he has a big weakness to fire.

Mannimarco is extremely powerful and resistant to most magic, except fire. Stand back and blast him with fire, dodging his attacks. If his AoE attacks hit you, he'll absorb your health. You can also try dodging the resurrected Nathyss or deal with him first. Nathyss, again, is weak to shock and normal weapons. I recommend avoiding levitating, as you'll move slower and it might be harder to dodge Mannimarco's ranged attacks.

Optionally, you can flee from Mannimarco instead, but you'll miss out on his staff. If you leave the place and re-enter they'll be gone.

Look around the shrine to find a chest with Mannimarco's spare robes.

Return to Gavin Vette.

Epilogue

Wait two to three days.

Report to Edwinna in Ald'ruhn.

The End

If you fled Mannimarco's boss fight, wait two to three days in the wilderness and an enthralled Gavin Vette will attack you.

If you return to where you fought Bolor Savel in the Savel Ancestral Tomb, you'll find a note left behind by Mannimarco.