You need to boost Montage Dragon's ATK to over 10k. Use The Ultimate Nightmare and Terror Incarnate for that. The combined level should be 34 or higher
I got 8k consistently using Yubel. Run lots of Glossy cards. Use Shien's Spy to give Montage Dragon to your opponent's field. Replace Fire King Island with the new one, Terror Incarnate will be destroyed so you can summon Ultimate Nightmare. Use Ultimate Nightmare to attack Montage Dragon
+3000 over 10k damage
+1000 effect damage only
+2000 win
+500 no damage/ comeback victory
+300 destroy 10 monsters
+200 use spell and trap
+100 special summon