Breed T-Rox + Bowgart on Plant Island during the Spooktacle season
Use a combination that includes one 3-element monster and one 2-element monster
Try Entbrat + Drumpler on Plant Island during the Spooktacle season
Try Bowgart + T-Rox on Plant Island during the Spooktacle season
Try other valid seasonal breeding combinations if available in your version of the game