"Toxic Spores" isn't a standard Magic keyword—it's flavor text or a specific card's name, not a defined mechanic. You may be thinking of Toxic, a keyword introduced in Phyrexia: All Will Be One. A creature with Toxic N means that when it deals combat damage to a player, that player also gets N poison counters (in addition to losing life). A player who accumulates 10 poison counters loses the game.
The nuance people miss: Toxic stacks with infect and proliferate, but Toxic creatures deal normal damage (life loss) alongside poison, unlike infect creatures which deal damage as poison only. So a Toxic 1 creature hits for life and a counter.
In Commander, Toxic is a slower alternate win condition. Proliferate decks weaponize it—each proliferate trigger adds poison counters across the board, accelerating toward that 10-counter kill while everyone's focused on damage and commanders.