My beloved Mumu (EDH / Commander)

The deck started as a super casual deck for Muldrotha the Gravetide, with just the cards I had. Then I improved on it, yet without looking for actual competitivity, and there it is now.

At some point, its wincon became the instant win brought by Primal Surge when the deck is only permanents and contains a Labman-like (here Jace, Wielder of Mysteries). The deck thus tries to control its way till it can cast Primal Surge, putting the whole library on the battlefield and then win through the static ability of Jace, Wielder of Mysteries (for a card will be drawn, either because of a trigger when all the crap enters the battlefield or because of the plus ability of Jace, Wielder of Mysteries.) Recently, I replaced Jace by Thassa's Oracle, as its triggered ability is safer than the survival of a Planeswalker. I then put Jace back in as its existence allows me to answer to potential answers by sacrificing creature (via cards like Ashnod's Altar) to trigger more draws via cards like Grim Haruspex.

An accidental combo was discovered with cards introduced for other purposes, which were Altar of Dementia (added to self-mill, which is almost like draw), Mazirek, Kraul Death Priest (which eventually got expelled) and Glen Elendra Archmage (there because of its use as a reusable counter-spell). The combo consists in sacrificing Glen Elendra Archmage to Altar of Dementia, and then ordering triggers from Persist and Mazirek, Kraul Death Priest so that Persist brings Glen Elendra Archmage back, then the +1/+1 counter from Mazirek, Kraul Death Priest removes the -1/-1 counter from Persist. Glen Elendra Archmage can then be sacrificed indefinitely until the opponents are milled to death.

The combo also works when replacing Glen Elendra Archmage with River Kelpie, and I have now replaced Mazirek, Kraul Death Priest with Mikaeus, the Unhallowed (this time, you simply alternate between Persist and Undying since both persistent creatures are non-Human). Those cards were also introduced for other purposes, respectively to draw cards and to protect the deck's creatures, for only a handful of them are Humans. Yet River Kelpie isn't as good as Glen Elendra Archmage for that combo, for it makes me draw as well, making it an anti-race towards mill death. A loop makes one opponent mill 4 et makes me draw 1, so with libraries approximately the same size, it's still winning, but because I draw with some regularity, there are risks.
Lately, I added Walking Ballista for its potential use as a damage output, and also because it gets us an additional endless combo with Mikaeus to kill (use a +1/+1 to deal 1, sac with Altar of Dementia to have it die (and mill an opponent), then it returns with a +1/+1 we can use to repeat)

Everything else in the deck is used either to control opponents' plays, generate Card Advantage to get the other cards as fast as possible, ramp to reach 10 mana faster, tutor for the combos, or protect the commander (or something else, sometimes).