Summon Ojama Knight or Ojama King as early as possible. They have enough defense to stall Mai's strongest monsters and with 0 attack Mai cannot use Amazoness Fighting Spirit to boost her attack.
After that just keep stalling until you deck out. Ojama Blue and Jar of Greed helps you get Ojamas out of your deck, King of the Swamp helps you search Polymerization in your deck. You can also use these cards to help fusion summon Ojama Knight earlier, if you have not yet.
This deck guarantees 8 rewards every time, unless you serious screw up. Summon the Labyrinth turn one and use the Rain of Mercy and Golden Ladybug cards to get at least 9500 LP. Use Cost Down to fill your board with 3 Labyrinth Walls in defense. Use 1 Pot of Benevolence to refill Mai's deck so she doesn't deck out. Use the remaining Pots to either stall to get your LP high enough or return an accidentally discarded piece of the last-turn combo into the deck. On the last turn, play Double Summon, Winged Dragon of Ra, Gravekeeper's Vassal, Secret Pass to the Treasure, and Union Attack.
You can replace Pot of Benevolence with card draw spells, but you risk losing them if Mai gets an Amazoness Sage out on the field. You can use other LP generation cards, but with this setup you only need Golden Ladybug to proc 5 times before you can use the 3 Rain of Mercy cards to reach 9500 LP.
+1000 (100 LP left from Ra's effect)
+500 (using Ra)
+200 (Ra is prismatic)
+3000 (10k damage)
+400 (spells and tributes
+1000 (using a god card)
Ultimate Ancient Gear Golem deck (99% winrate, 6-7k pts)
-Summon asap, stall long enough for Gravity blaster to boost his attack to well over 10k, (he deals damage through defense penetration)
-You need 11500 attack if she has a high defense amazon down, or 10300 attack if she has the paladin down
-Be mindful that you will be forced to attack the tiger if he's there, so if you have a gear beast or other golem in your hand, in the last turn you can summon it to destroy him and then attack the paladin if she's there (if it will help you get the 10k damage)
2x Ancient Gear Golem
1x King of the Swamp
1x Ancient Gear Box
3x Ancient Gear beasts
2x Ancient Gear Soldier
2x Gravity Blaster
1x Bolstering wind (get rid of the amazon that destroys a spell/trap, or use it in the last stage to get an extra boost)
1x Floodgate Trap hole
1x Mirror Wall
1x Impenetrable Defense
1x Draining Shield
Well, she does have 2 Fighting Spirit, so it's certainly possible for her to get over Gate Guardian. I wouldn't say it's easy for her to do so, though. And Labyrinth Wall should be straight impossible for her to get over.