https://aetherhub.com/Deck/keju-combo
Introduction
Why play one hyper-efficient combo when you can play all the combos?

The goal of this deck is to generate infinite mana,+1/+1 counters, or creature untaps, and then do silly things to win the game on the spot. Most of this is driven by the commander Experiment Kraj, with Quicksilver Elemental playing a supporting role. I've tried to keep things on a budget, while also playing some of the random terrible cards that I already have in my collection. The deck keeps low to the ground, with the intent to put the commander on field on turn six or so. This won't win any cEDH games, but hopefully you'll find it a lot of fun.



The Combos
Most combos consist of three parts:

1. The commander, Experiment Kraj or backup ability-thief Quicksilver Elemental.

2. A creature or land that taps for multiple mana. Blue mana is prioritized, since five of the six untappers require (U).

Ilysian Caryatid, Incubation Druid, Gyre Engineer, Oasis Ritualist and Ley Weaver tap to generate two or more mana without setup, while Kiora's Follower can untap a single land. Krosan Restorer straddles the line, generating infinite with Simic Growth Chamber and lands enchanted with New Horizons or an Island enchanted with Wild Growth when there are fewer than 7 cards in the graveyard, and going infinite with any three lands when the threshold value is reached.

3. A creature able to untap itself.

Horseshoe Crab, Pili-Pala, Leech Bonder, Freed from the Real and Simic Ragworm fill this role. Each untaps for one mana (mostly U).



Freed from the Real is also a two-card infinite mana combo with any of the creatures that can generate two or more mana.



+1/+1 Counters
Kraj only gains the abilities of creatures with +1/+1 counters on them. While it can tap itself to put on that counter, it's generally best if the creature already has the counter when Kraj comes into play. There's a few ways to ensure that:

Renata, Called to the Hunt and Bloodspore Thrinax give every incoming creature one or more +1/+1 counters. Durable Handicraft does the same for (1), Zameck Guildmage for (UG), Retreat to Kazandu does so on landfall, Hall of Oracles does so on after an instant or sorcery spell is cast, and Oran-Rief, the Vastwood gives a counter to incoming green creatures, while Ivy Lane Denizen puts a +1/+1 counter on any creature whenever a green creature comes in. New Frontiers is a one-off effects, while Neoform is gives a one-off birthing pod effect that comes with a +1/+1 counter. Ridgescale Tusker puts counters on each of your creatures in play, and Durable Handicraft can do the same, if need be.



Wincons
Tap Experiment Kraj to put infinite counters on all your creatures, then just go face.

With infinite untaps Experiment Kraj can channel Prodigal Sorcerer to do infinite damage to every player and every creature they control, at instant speed.

Infinite untaps also makes Teferi more annoying than usual, allowing his Disruptive Student form to counter every spell your opponents play.

Infinite mana allows Lore Weaver to kill every opponent by making them draw their entire library +1.

Ambassador Laquatus will skip the drawing, and just mill out every other player.

Finale of Devastation is definitely overkill, but it gives haste! Also, infinite power and toughness.

Jade Mage is the perfect mana sink, making blockers in the early game and infinite saprolings once a combo is achieved.

Animation Module normally just makes chump blockers.  With infinite mana and either Renata, Called to the Hunt, Bloodspore Thrinax or Durable Handicraft, the tokens go infinite.

With infinite Kraj untaps Scurry Oak can make infinite squirrels. It'll do the same if you ever get the Oak and Ivy Lane Denizen on the field at once, then play a green creature (or have Ivy Lane Denizen already on the field and play Scurry Oak).



Protection
To keep Experiment Kraj alive we have Intervene, Stubborn Denial, Autumn's Veil, Spell Pierce and Barkhide Troll. Nurturing Licid performs double duty, either enchanting Kraj and giving it the ability to regenerate, or allowing Kraj to turn itself into an enchantment at will, dodging Path to Exile-style effects. Inspiring Call is both card draw and a way to guard against boardwipes during the setup turns.

The best protection is to assemble the combo from out of nowhere, which is why Emergent Zone, Vernal Equinox, Savage Summoning and Crashing Drawbridge are also in the deck. Vivien, Champion of the Wilds, Yeva, Nature's Herald, etc. aren't in the deck but can be substituted in to also give flash, and of course Swiftfoot Boots and Lightning Greaves offer other haste effects. Tidal Barracuda is a tentative inclusion; it gives everything every player casts flash (opening up instant-speed boardwipes), but prevents spells from being cast on your turn.



Tutors
Neoform is the best single creature tutor. Whatever we search for comes into play with a +1/+1 counter, ready to go, and the base list includes untappers and 2+ mana creatures at 2, 3, and 4 cmc. Evolutionary Leap is much more of a roll of the die, but it helps convert otherwise useless creature tokens into valuable combo pieces. Uncage the Menagerie on 3 will find a crab and a two-mana source, with room for one of the three-mana wincons (Prodigal Sorcerer or Ambassador Laquatus). Incubation // Incongruity isn't good, but it is cheap, and helps us both dig or deal with a single threat.  Finale of Devastation is great, and also about half the deck's cost.  It can be pretty easily substituted for Chord of Calling, but I have the card from a War of the Spark prerelease.



What about X?
I've put every other relevant card that I could find in the maybeboard.  I don't think there's any wrong way to build this deck (I went on a pretty long tangent at one point, collecting land untappers and enchantments that made lands tap for more than one mana), and it's definitely better to work with the cards you have than buy 60-odd new ones.



A few wincons didn't make the cut, either because they were objectively terrible or because giving creatures infinite +1/+1 counters made them somewhat superfluous.

Temporal Adept is in the first category. Infinite mana and untaps lets Experiment Kraj channel Temporal Adept and bounce every permanent your opponents control. Including lands.

Wildheart Invoker can give infinite power/toughness and trample with only colourless mana. Probably worth including if you have a Kinnan or other non-Kraj/Quicksilver infinite mana combos.

Squirrel Nest makes infinite tokens with infinite land untaps.  Jade Mage is superior in just about every way.

Laboratory Maniac, Thassa's Oracle and Jace, Wielder of Mysteries are just boring.



Upgrades
Keeping decks cheap keeps food on my table, but there's always room for more powerful cards.  I don't think there's a deck that Mana Crypt wouldn't make better, and Pemmin's Aura does everything Freed from the Real does and more. The deck feels pretty solid as-is, but if you want to go splurge on Earthcraft be my guest!