Here's a written walkthrough:
1. You will need to get to the third hideout in the evil playthrough.
Check out the link below on how to get to this point!
2. Talk to the first guy in the hideout, who will tell you to go to the very first area to kill Tancred.
3. Go there, and sink the boat with the Thunderstorm ability, and kill Tancred.
4. Tancred will flea, to which you will need to go to the bottom left of the map after completing the main quest in the third hideout.
5. Enter the now open hideout in the bottom left, and talk to Robert, to start the assault on Darkov.
6. Play through the assault. There are 2 mini bosses. They are all in the video.
7. Tancred will be the last boss you kill.
- Tancred has a lunging spin attack, a jumping and lunging spin attack, as well as spear jabs. He's very fast-paced and does not leave a lot of distance before quickly attacking again. My recommendation is to use the hellfire ability and shoot fireballs at him while consistently being agile, and typically jumping over his spin attacks. He is pretty relentless.
How to get here can be found in the ultimate evil playthrough guide: