If you can special summon "Obelisk the Tormentor", its effect allows you to destroy all of your opponent's monsters, at the cost of 2 of your monsters and preventing "Obelisk" from attacking and since he was Special Summoned, he is destroyed in the End Phase. This makes "Obelisk" a perfect monster to Tribute Summon "Great Maju Garzett", replacing an otherwise worthless monster with an automatic win (8,000 standard life points and no monsters protecting them), barring any Spells or Traps.
Remember to have couple copies of "Mystik Wok" handy. If "Great Maju Garzett" would be destroyed, you can gain a high amount of Life Points while effectively wasting your opponent's effect.
This card works well with "Corrupted Keys", as you can tribute the free tokens it gives you to make "Great Maju Garzett" gain significant attack without having to fear your tokens disappearing when your Xyz Monster is destroyed. Additionally, "Great Maju Garzett" can attack directly, unlike the token he tributes.
After using the effect of "Summoner of Illusions" to Special Summon "Blue-Eyes Ultimate Dragon" or any Fusion Monster with 4000 or more ATK, tribute it for a "Great Maju Garzett" with at least 8000 ATK. This can result in an OTK, given your opponent has an empty field.
This card is a great way to "reuse" monsters which suffers from a handicap after attacking, such as "Goblin Attack Force", "Giant Orc" and "Chainsaw Insect". All of these can be normally summoned and have an ATK of 2200-2400, giving "Great Maju Garzett" 4400-4800 ATK easily.
If this card gets summoned early by sacrificing a monster with at least decent ATK, your opponent will likely be setting monsters face-down. If this happens, you can combo "Light of Intervention" (to keep him from setting monsters) and "Final Attack Orders" so he/she will be wide open for massive damage.
Sadly, you cannot use "Megamorph" to increase its ATK, because it relies on the original ATK of the equipped monster, which is treated as 0. Similarly, trying to boost a monster's ATK with card effects generally doesn't affect the power of "Great Maju Garzett", as it uses the original ATK of its Tribute fodder to calculate its own ATK.
If both "D.D. Survivor" and "Macro Cosmos" are out, you can Tribute "Survivor" for this card, effectively gaining a 3600 ATK monster without losing any card advantage. Highly effective in a Removal Deck.
Another great choice is "Malefic Rainbow Dragon": it can be recycled with "Recurring Nightmare", exactly together with "Great Maju Garzett", so you can virtually re-Summon it immediately, if you have another "Rainbow Dragon" in your hand or Deck.
Cards that can be used or can get strong monsters for the summoning of "Great Maju Garzett" include:
A fairly easy way to score an OTK in a duel is to get your opponent to destroy "Mystic Tomato" in battle to Special Summon "Cyber-Stein". On your turn, pay 5000 Life Points to Special Summon "Blue-Eyes Ultimate Dragon". Next, tribute "Blue-Eyes Ultimate Dragon" to Special Summon a "Great Maju Garzett" with 9000 ATK. Try to prevent your opponent from countering and also try to end the duel on the same turn with "Great Maju Garzett". If your opponent tries to making it leave the field, use "Mystik Wok" for an easy 9000 Life Points, up to 4000 more than the cost of beginning the combo.