Used the following for 700+ favor per set, successful sparks:
1. Thief Imp Philum
2. Twinkle-in-the-Dark Mushroom
3. Trumpet Bell Poison Mushroom
4. Cloudy Rain Mushroom

Spark fails are near impossible with him. Suggest new game if that's the case.

Evildousharm mentioned in his video that 1000 amity with this person increases the chance of getting better workers