Talk with Wyll while he is training children to fight at the Tiefling Camp near Emerald Grove. Invite him to join your party or meet you at camp.
Invite Wyll to join your party when you travel to Moonrise Towers, since his father is rumored to be a prisoner there. When you take a long rest in the Ruined Battlefield, Mizora will stop by your camp again. This time, you may detect a way out of Wyll’s pact if your perception check succeeds.
You will find the prisoner to release just north of the Tadpole Center in the Mind Flayer Colony under Moonrise Towers in Act 2. Free the prisoner to continue progressing Wyll’s questline.
After walking through Wyrm’s Rock, you will find Mizora on the other side of the bridge. Talk to her again and find out that Wyll’s father is attending the coronation. After defeating Gortash, speak to Mizora again. This time she will agree to meet at camp. When you return to camp, start a long rest and talk with Mizora. She will offer Wyll to extend his contract for a tempting reward or break it. Choose “Then break it already…” followed by “Break the pact Wyll…” to free Wyll from his contract and unlock the Loophole achievement.