Otaria was actually the site of two different Magic the Gathering blocks in the early 2000s. In lore/fluff, it is a smallish, remote continent on Dominaria which was less affected by the Phyrexian Invasion than other places. This remoteness also means that it has a rather different style of cultures, including plains nomads and a decadent, corrupt Cabal that dabbles in creating abominations, and some different creature types that you don't usually see in other black-bordered sets. Actual support for Squirrels as a tribe? It's more likely than you think!
Odyssey, Torment, and Judgment were sets with graveyard-based mechanical themes. The obligatory keywords were threshold, where a card gains more abilities once you have seven cards in your graveyard; madness, where you can cast a card for an alternate cost if you would discard it for any reason; and flashback, where you can cast a card from your graveyard for an alternate cost.
Torment and Judgment were the only sets so far that had an intentional color imbalance. Torment had more black cards and fewer in green and white, and this was reversed for Judgment.
Onslaught, Legions, and Scourge were sets with a tribal (creature types matter) mechanical theme. After Odyssey's sojourn into oddities like squirrels and cephalids, this block saw the return of more traditional tribes such as goblins, elves, slivers, and dragons. (Merfolk, though, would have to wait for Lorwyn.)
Onslaught introduced a couple of keywords of its own, most notably morph, which allows you to play a card face-down as a 2/2 creature for three generic mana instead of its usual manner and possibly later flip it into its usual mode for another cost.
|Settings of Magic: The Gathering|
|Pre-revisionist:|| First Magic Sets - First Urza Block - Arabian Nights |
Legends - Homelands - Ice Age - Mirage
|Weatherlight Saga:|| Portal Starter Sets - Second Urza Block |
Tempest Block - Masques Block - Invasion Block
|Post-Weatherlight:||Otaria Block - Mirrodin - Kamigawa - Ravnica - Time Spiral|
|After the Mending:|| Lorwyn - Alara - Zendikar - New Phyrexia |
Innistrad - Return to Ravnica - Theros - Tarkir - Eldraine - Ikoria
|Two-Block Paradigm:||Kaladesh - Amonkhet - Ixalan|
|Never in a standard set:||Fiora (Where the Conspiracy sets take place) - Kylem (Battlebond)|