Ixalan underground. Four decks for the four factions: Pirates, Vampires, Merfolk and Dinosaurs.
Reveal the top card of your library. Land goes to your hand, anything else stays on top and the creature gets a +1/+1 counter. The Merfolk deck turns that into both a growth engine and card selection.
Exile cards from the top of your library until you hit a nonland card with a small enough mana value, then cast it free or put it in hand. The Dinosaur deck uses it to cheat large creatures into play.
Once you control ten or more permanents you get the city blessing, permanently. Several cards in the set switch on at that point, which suits decks that go wide.
Descend counts cards in your graveyard and pays out at set thresholds. The Pirate deck mills its own crew, so the count climbs quickly.
The Lost Caverns of Ixalan splits along the same four faction lines the plane always has: Pirates, Vampires, Merfolk and Dinosaurs. Each Commander deck gets one.
Explore is the mechanic that ties the plane together, and it is still the best of them: card selection and a +1/+1 counter on the same trigger. Discover is the new one, and it is effectively cascade with a ceiling, which is why the Dinosaur deck can put something huge on the battlefield well ahead of schedule.
Discover is worth reading carefully before you play it. Unlike cascade you get the choice of casting the card free or putting it in your hand, and the mana value cap means the deck has to be built with a curve that gives you good hits. Pantlaza discovering into a five drop is a swing; discovering into a land you cannot cast is a wasted attack.
The four decks also cover four completely different resources: counters, graveyard count, permanents on board and creature deaths. If you want a single product that demonstrates four ways to build a Commander deck, this is a good one to point at.
Veloci-Ramp-Tor is the most fun to play blind, since discover makes every attack a surprise. Blood Rites is the most consistent of the four.
Admiral Brass, Unsinkable
A Grixis Pirates deck from The Lost Caverns of Ixalan that mills its own crew and reanimates them for combat. Admiral Brass, Unsinkable brings a dead Pirate back every turn, then the tribe swarms in for treasure, steals, and extra damage.
Clavileño, First of the Blessed · Carmen, Cruel Skymarcher
An Orzhov vampire aristocrats deck led by Clavileño, First of the Blessed, sacrifice vampires to create flying Vampire tokens, drain opponents on every death, and win through an ever-growing air force of undying vampires.
Hakbal of the Surging Soul · Nicanzil, Current Conductor
A Simic Merfolk counters deck led by Hakbal of the Surging Soul, explore to put +1/+1 counters on your Merfolk, stack them into enormous threats, and win through an unblockable counter-loaded board enabled by Herald of Secret Streams.
Pantlaza, Sun-Favored · Wayta, Trainer Prodigy
A Naya dinosaur tribal deck led by Pantlaza, Sun-Favored, discover your most powerful dinosaurs for free, trample through opponents with enrage triggers, and win through unstoppable prehistoric threats that refuel the board with each combat.