Elements unite actually work for the final boss. I managed to do all 3 missions in one duel using this list: 1x Pyrorex 1x Beast of Serket 3x Brushfire Knight 2x Crystal Seer 2x any normal FIRE monster 1x Riryoku 1x Shooting Star Bow - Ceal 1x Temple of the Kings 2x White elephant's gift 2x Any field spell 1x The Humble Sentry 1x Gift of the Martyr 3x Jar of Greed 1x Ble-Eyes Ultimate Dragon The decks works like most normal Elements Unite decks, get Gate Guardian out and draw into your combo. In this case, however, set your crystal seers and your fire monsters and let the boss destroy them, but be very careful so that you won't be forced to mill Pyrorex with Brushfire. The final combo works by summoning pyrorex, activating Temple, tribute Gate Guardian to normal summon Serket, activate temple's effect to summon Blue-Eyes Ultimate from the fusion deck, use rirsoko on ultimate, give power to pyrorex, then use gift of the martyr, tributing Ultimate and giving power to Pyrorex, finally give ceal to pyrorex and attack directly for 8550 direct damage. If you managed to activate both field spells and waited until it was 3 or less cards in your deck you should have all 3 missions done. IMPORTANT NOTE: this isn't a perfectly safe build, it's still possible that the boss summons Pyre of malice and destroys one of its own monsters to pop the Michizure on your monster. I hope this still helps someone. gl for those still doing the event.