I am going to start off by declaring that I do not like the nature of this deck. It goes against every aspect, impressions and everything I know and adore about the game. This deck ends games quick. This deck antagonizes opponents and tramples on the good natured players whom after a long, depressing week of work, just want to have fun. And this deck will never suffer from power creep.
However, one of my longtime local players, that was struggling to achieve any sort of victory through his Yugioh career, adopted this deck only last year and has been pocketing wins back-to-back! I was seriously impressed. Although we have managed to convince him to finally try other interactive decks (for our sanity), this article will be crafted in recognition of such a feat.
If you are a returning player, or simply just have difficulty getting back into the game because everything is too complicated, this deck might be for you!
This will be a general review of the Gren Maju deck, with an assumption that the reader has already has an understanding of the game's fundamentals.

Introduction

Right into the news, I will introduce the most important card of this deck.

Gren Maju Da Eiza is a simple level 3 monster that rapidly grows in stats for each banished card. So the gameplan is simple: Banish at most 20 cards, then poke your opponent with a game-ending 8000ATK, and still have 15 minutes leftover till the next round. It really is that simple!
But to achieve this, the player should recognize the two problems this deck faces: banishing that many cards, and actually having this monster on board. Thankfully, as the game develops more and more, this deck's consistency will only (unfortunately) improve.
The following will cover core cards essential to augmenting Gren Maju.

I don't need these.

Banishing cards from your extra deck means you will not be using them for the rest of the entire game, but that should not be an issue if you are looking to end the game instantly. As such, these cards fuel your Gren Maju, while generating advantage on their own accord.
While banishing cards may seem like an extreme downside, the player will not have lost any card advantage!

Monsters Banishing

• Eater of Millions
  Eater of Millions is a great way to remove opposing monsters, just by completely removing them from the field! Additionally, given enough banished cards, this little fella can easily inflict 2000+ damage on the opponent if left unchecked! His effect applies once on either player's turn, making it both a great aggressive and defensive tool.
  This voracious little cretin will cost you a minimum of 5 banished cards from your Extra Deck, but you can instantly remove your entire Extra Deck just to fuel Gren Maju.
  
• Gizmek Orochi, the Serpentron Sky Slasher
  Orochi will constantly summon itself from your hand or grave with a meager cost of 8 top cards from your deck. While its effect is not as impressive as Eater of Millions, this monster will slowly fuel Gren Maju's requirement by constantly banishing in 8s, until you suddenly find 24+ cards gone from your deck and Gren Maju at full power. As a simple recurring body, Orochi can easily synergize with many techs due to its favorable level, type and attribute.

Spells Banishing

• Pot of Desires
  This controversial card has managed to claim a permanent spot with Gren Maju. The reason is simple: It draws 2 cards, and your 10 removed cards fuel Gren Maju. The only drawback is banishing all 3 of your Gren Maju, but usually the rest of the deck should be able to win the game anyway!
  
• Pot of Extravagance
  This card might be even more controversial then Desires! Even though the cost is from the Extra Deck (meaning no chance of banishing a Gren Maju), the drawback of not being able to draw more might hurt certain variants of the deck. However, more draw power is always appreciated.

Now that you know it is that simple to charge Gren Maju to full capacity, and the cards supporting it are also generic, so how do you go about building the deck? Interestingly, there are two contrasting variants that stand out as of this article.

Decklists

Danger!? Gren Maju?

This is the TCG's aggressive approach to Gren Maju.
By stuffing several Dangers into the deck, the deck aims to activate Dangers and draw into Gren Maju, conveniently using their effects to pick away at the opponent's board. The end board will usually be several high-power Dangers accompanying Gren Maju to end the game within the turn.
This OTK variant will always opt to go second.

Inspector Gren Maju 🧐

This is the OCG's passive approach to Gren Maju.
By stuffing unfair monsters and punishing Traps into the deck, the player will slowly suffocate the opponent until Gren Maju is drawn. Sometimes, the game will be simplified into just Inspect Boarder bashing the opponent till defeat...
This Stun variant will always opt to go first, but Gren Maju may suddenly conclude the game going second.

Gren Maju has such differing playstyles, that it might be difficult to pinpoint the deck's exact win condition until Gren Maju itself actually appears! Fortunately, this deck is not all powerful.

Gren Maju and Fren Majus

Despite the above lists optimizing the use of Gren Maju, there are other techs that have supplemented Gren Maju in the past! Take a look and consider if they are worth of use.

• Necroface
  In conjunction with Gold Sarcophagus, Necroface banishes 5 cards from each player's deck, potentially banishing an opponent's key card.
  Necroface can also recycle banished Gren Majus, and power itself up to ridiculous numbers!
  
• Brotherhood of the Fire Fist - Horse Prince
  This is the most consistent way of ensuring Gren Maju's presence, but may take some effort to summon. Maybe an Ash Blossom with a Danger!? Tsuchinoko?
  
• Inferno Tempest
  In conjunction with Grinder Golem, this used to be the only way to play a Gren Maju deck. Unfortunately, one performed far too much for its own good, and Gren Maju has found a new style. This spell might be too much work now to get a return out of.
  
• Golden Castle of Stromberg
  Honestly, this card has too much text!? But it's still important to learn? Golden Castle sacrifices your normal summon to get Hexe Trude and pick apart boards. This may conflict with Gren Maju, but it allows the deck to have different win conditions. The cost for maintenance is beneficial, and nobody reads the last effect...
  which makes you almost immortal!? Destroy all your opponent's attacking monsters and laugh at their confusion!!!

Countering Gren Maju

The easiest counter to Gren Maju is effect negation. A simple Infinite Impermanence or Forbidden Droplet results in a 0ATK Gren Maju. Artifact Lancea can also stop it from powering up for a single turn, even shutting off their Pots of Drawing! However, Gren Maju is backed by its variants which will try to counter this aspect.
Against the Aggressive Gren Majus, Droll & Lock Bird will deny one turn, which you can use to push the game back in your favor.
Against the Passive Gren Majus, you might need to stockpile S/T removal such as Harpie's Feather Duster and Red Reboot, but be sure to pack effect negation/spot removal for problematic monsters like Inspect Boarder and Thunder King Rai-Oh.
Lastly, against all Gren Majus effect negation is key to shutting them down. Since Gren Maju's attack boost is an effect, negating it will render it weak and useless.

My Thoughts and Conclusion

I hate this deck so much. I might even hate it more then Altergeist if more people start to play this.
However, this is a cheap deck to build. It is simple to understand, and most importantly, it gives players a chance to beat back stinky meta players at casual locals.
I recognize that out there even, there are players who adore this deck's playstyle. In fact, this deck has a recognized top, which you can read about here.
To you, I hope my article may grant you a better insight to Gren Maju. Or unfortunately, spread awareness of this abomination.
This article is dedicated to the single Gren Maju player in my country who keeps defeating us ;)