So like I mentioned, I've been getting into cEDH (competitive 4-player Commander). Some of the decks that are notably rather strong in the cEDH setting are also highly unusual in other respects when it comes to how Magic decks work and what they do. The 100-card singleton constraint would, on its own, would seem to mostly rule out illuminating decks. But the combination of the 40 starting life total, the massive card pool, and the commander mechanic go some way to turning that around. Before I begin, I want to provide a brief note about cEDH and why I find it worthwhile. The competitive version of what was originally envisioned as a casual multiplayer environment has been much maligned. The thing is, casual EDH as a format is actually rather, well, bad. The format's "official" Rules Committee and Wizards of the Coast have repeatedly worked at cross purposes, with the Rules Committee making changes to guide the format one way while WotC prints new cards in commander products that pulls the format in a different direction. The ban list is haphazard and early iterations of it came with a constant caveat of something about how it was all just suggestions to help you out but if cards are a problem in your local playgroup, you should ban them. That pretense has since been dropped, but I've never known commander players to play primarily within a specific local playgroup that curates its own separate ban list. Essentially everyone is using the official list with all of its quirks. The format is rather broken and players run into problems of disparate power levels all the time. Sol Ring might not seem overbearing in a precon, but it's rocket fuel in a finely-tuned combo deck. In all of this unfortunate chaos, some players either with substantial investment in their decks or with proxies, focus on taking commander power levels to the extreme. And so they've got an extremely fast-paced format that is dymanic, with lots of interaction and different strategies. These decks aren't meant for casual commander games: they're not even optimized to beat the decks in casual pods! In general, a cEDH deck would be potent in a casual pod, but it wouldn't be the best weapon to take down casual games anyway. These decks are better optimized to battle each other, and in that context, maligning them strikes me as pointless. I think a lot of the hate thrown at cEDH is based on the incorrect assumption that the guy being a scumbag moron with a powerful deck trouncing local casual scrubs is using a cEDH deck. But he's probably not and his deck would probably lose badly against true cEDH decks.
I don't know how many of these decks I'll try to include in the Hall, but at least a few are ones I've found to be illuminating. Decks in cEDH run a gamut from ones that absolutely rely on their commander to ones that are basically 99-card decks and only have the commander as a distant backup plan. Surprisingly, neither approach is truly superior. Anyway, while this is primarily a casual site, I suspect that cEDH is one competitive environment that most of the people here would at least find intriguing to observe, although you may or may not participate in it yourselves...
Let's start with one I already touched on here at the CPA.
Deck Name: Chain Veil Teferi
Magic Format: cEDH
Insight: In 2014, Wizards of the Coast created special planeswalkers that are allowed to serve as commanders. Earlier that year, they'd made The Chain Veil, an artifact that lets planeswalker abilities be activated extra times in a turn. This deck exploits a loop in which Teferi, Temporal Archmage is cast from the command zone repeatedly, but generates enough extra mana to continuously pay the commander tax and recast it. The loop requires some sources that tap for 2+ mana and some knowledge of the counterintuitive rulings on the functionality of The Chain Veil, but this is the only loop I know of that exploits both a planeswalker and the command zone. The combo is successful in cEDH because it is a compact and flexible kill condition that can be assembled in multiple ways, so it forms the core of the most popular monoblue control-combo deck in cEDH.
Deck List (05/27/2019)
Commander:
1x Teferi, Temporal Archmage
1x Academy Ruins
1x Ancient Tomb
1x Back to Basics
1x Baral, Chief of Compliance
1x Basalt Monolith
1x Blast Zone
1x Brainstorm
1x Buried Ruin
1x Chain of Vapor
1x Chrome Mox
1x Copy Artifact
1x Counterspell
1x Cursed Totem
1x Cyclonic Rift
1x Delay
1x Dig Through Time
1x Dispel
1x Fabricate
1x Fact or Fiction
1x Fellwar Stone
1x Flooded Strand
1x Flusterstorm
1x Force of Will
1x Gilded Drake
1x Gilded Lotus
1x Gitaxian Probe
1x Grafdigger's Cage
1x Grim Monolith
1x High Tide
1x Impulse
1x Intuition
1x Inventors' Fair
21x Island
1x Legacy's Allure
1x Mana Crypt
1x Mana Drain
1x Mana Vault
1x Memory Jar
1x Mental Misstep
1x Merchant Scroll
1x Misty Rainforest
1x Mox Diamond
1x Muddle the Mixture
1x Mystic Remora
1x Mystical Tutor
1x Narset's Reversal
1x Narset, Parter of Veils
1x Negate
1x Pact of Negation
1x Polluted Delta
1x Ponder
1x Power Artifact
1x Preordain
1x Pull from Tomorrow
1x Pulse of the Grid
1x Reshape
1x Rhystic Study
1x Rings of Brighthearth
1x Sapphire Medallion
1x Scalding Tarn
1x Sensei's Divining Top
1x Sleight of Hand
1x Sol Ring
1x Spellseeker
1x Stasis
1x Stroke of Genius
1x Swan Song
1x Tezzeret the Seeker
1x The Chain Veil
1x The Tabernacle at Pendrell Vale
1x Thran Dynamo
1x Time Spiral
1x Timetwister
1x Transmute Artifact
1x Trinket Mage
1x Ugin, the Spirit Dragon
1x Verity Circle
1x Whir of Invention
1x Windfall