Power of the Tributed When you sucessfully Tributed Summon "The Winged of Ra", its ATK will becomes the sum of the ATK of the Tirbuted Monsters, and its DEF will becomes the sum of the Tributed Monsters.
Summon Gate Guardian right away. Don't destroy Yami Yugi's monster, and don't summon or set any other monster with low attack unless you plan on using White Elephant's Gift right away. Yami Yugi's Phantom Beast Rock-Lizard will destroy it, inflicting 500 damage to you and lose you the duel. Pass the turns and use the draw cards, perform fusion summon and setting at least 1 Spell Reclamation before the last turn. You can use any normal monster that you have, it doesn't need to be glossy.
Summon unhappy girl as soon as you can, and pass the turns to stall the duel. Get BEUD out before the last turn and leave a monster slot open for vassal. Use vassal and union attack combo on the last turn.
If you don't have union attack, you can use Cu Chulainn with Blue-Eyes White Dragon, ritual weapon and riryoku instead.