Decks I've been Playing: Acererak Storm
I am once again doing perverse things in Brawl. Acererak the Archlich is a very silly card from the crossover D&D set Adventures in the Forgotten Realms. It uses the 'venture into the dungeon' mechanic which is probably the nadir of 'reading the card explains the card' in Magic design; a mechanic that you can't really understand without a brief explainer and several extra gameplay-aid cards.
In short, the 'dungeon' is a little linear path (with branches and rejoins), depicted on a card. When you venture into the dungeon for the first time, you choose one of the three available dungeons and play it. Every subsequent time you 'venture into the dungeon', you advance one step.
Acererak's intended design is that you combine him with the Tomb of Annihilation to 'quickly' get a 4/4 and a 5/5 with a powerful ability into play after casting Acererak only three times. When played as intended, it's not a very good card, and this is absolutely not how this deck intends to use it.
Instead, you venture into one of the other two dungeons, specifically the Dungeon of the Mad Mage. As completing this one doesn't cause Acererak to stick, you can keep recasting Acererak from your hand indefinitely forever. The deck's intended play pattern is to mulligan aggressively to find a cost-reduction effect like Cloud Key and just start casting Acererak as many times per turn as possible, gradually accruing value.
The final ability on the dungeon gives you three draws and a free spell; combined with the scry effects in previous dungeon steps, that lets you churn through your deck to find more cost-reduction effects and fast mana to cast Acererak more times, until you win with either Tendrils of Agony or Aetherflux Reservoir.
This is a deck premise that has been lurking in Brawl for a long time, but it's really become a real thing you can do in the last year with the addition of a good half a dozen cards that combo with Acererak. Modern Horizons 3 brought useful reprints Jet Medallion and Urza's Incubator to Arena for the first time, letting the deck play enough cost-reduction effects to consistently find one.
The bottleneck here really is finding Relic of Legends (or one of a couple other similar effects), which deals with the single black mana in Acererak's casting cost which otherwise can't be reduced away by Medallion effects.
More recently, Sibsig Ceremony was printed to add another cost-reduction effect with the added upside of creating an army of zombies as you cast Acererak 4 or 5 times a turn, giving the deck another dimension.
This style of combo deck is hard to make work in Brawl because the format is singleton and doesn't have access to most ritual spells used to enable the Storm mechanic. Acererak provides a different angle; instead of rituals and cantrips, you use a card that can be infinitely recast alongside cost-reduction effects. Like other storm style decks, it's very hard to interact with as you don't really rely on having a creature in play and creature interaction can't really stop you. Like a lot of the brawl decks I play, it's designed to prey on the uninteractive big-mana decks built around casting a seven-mana commander that generates an unsurmountable amount of value.
If you'd like to try this nonsense for yourself, here's a Moxfield link.