Hello, here's my favorite format, Bad Tribal:

Any creature type in Magic outside of a select few are eligible to be used (more on that later). You build a (minimum) 60 card deck (no sideboards are used) that has at least 25 creatures from the chosen Tribe. Everything else in the deck has to follow the current Modern format rules (including Banned List), but your tribe's creatures can go back to Alpha, if you want to, as any sets are allowed, including special sets like dual decks & commander! (keep in mind that OTHER creatures in your deck that aren't related to your tribe have to be Modern legal).

Now, for the Banned Tribes List:

(some are color-specific, for example, you can't use BLUE Wizards, but any other color Wizards are fine): Beasts, White Clerics, Elemental, Green Elves, Blue Faeries, Zombies, Red Goblins, Merfolk, Slivers, Soldiers, Black Vampires, and Blue Wizards. No creatures from these tribes can be used in this format. Note that Shapeshifters that have the "Changeling" keyword ability are exempted from this rule and may be used to represent any tribe (they'll definitely help you in a Kobold deck!)

Also; you can't have ANY cards of the banned tribes in your deck (with the exception of changelings.)! For example: if you're make an assassin bad tribal deck, you can't use Guul Draz Assassin even if he is your only black vampire!

There is a 1-card banlist: Riders of Gavony.

Sideboards are not used to to problems with keeping the 25 creatures.