Use sonic bombs and a thunder attribute weapon . Raw will work too. Also bring 10 megapotions , potions, mega juice, and power seeds. Listen man the monoblos isnt really that hard if you watch him closely. Lead him into cliffs he ll get stuck. After his horn's off that tactic wont work on him anymore so bring fash bombs also so you can slow him down in his tracks.
technically it will stop him in his track, oh and btw sonic bombs wont work on him when he is enraged