It's very strong with Black effects that force everyone to discard
If you're looking for solid turn-2 plays that fit into almost any deck, these are hard to beat
Fischer Standard Legal Alchemy Legal Pioneer Legal Historic Legal Modern Legal Brawl Legal Legacy Legal Comp
The term "defending player" in the myriad rules (or any other ability of an attacking creature) refers to the player the creature with myriad was attacking at the time it became an attacking creature this combat, the controller of the planeswalker the creature was attacking at the time it became an attacking creature this combat, or the protector of the battle this creature was attacking at the time it became an attacking creature this combat
specifically, each color making war on itself, with two major tribes for each color
Alongside an excellent set of reprints, Mind Flayarrrs has some quality new cards, including Aboleth Spawn, a hilariously annoying ability copier that turns enemy enter-the-battlefield effects against them