I am trying to recruit Slugosaur with Yukken Z and Rikken double pincers with Suoh and Gatz, but sometime I can't recruit the monster with Yukken and Rikken activated negotiator pro 4 times. If I do the math 5% x 4 x 8 = 160% but it doesn't guarantee monster will drop. I usually activated Augment from Gatz and PalpaZ to kill it in 1 turn. Maybe I did too much damages or S/L the game caused it to become bug. That's just my theory.