StormStorm is a triggered ability that functions on the stack. “Storm” means “When you cast this spell, copy it for each other spell that was cast before it this turn. If the spell has any targets, you may choose new targets for any of the copies.”
If a spell has multiple instances of storm, each triggers separately. (CR 702.40) (When you
castTo cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if they have priority. See rule 601, “Casting Spells.”
To cast a card is to cast it as a spell. (CR 701.5) this spell, copy it for each spell
castTo cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if they have priority. See rule 601, “Casting Spells.”
To cast a card is to cast it as a spell. (CR 701.5) before it this turn.)
ProliferateTo proliferate means to choose any number of permanents and/or players that have a counter, then give each one additional counter of each kind that permanent or player already has.
In a Two-Headed Giant game, poison counters are shared by the team. If more than one player on a team is chosen this way, only one of those players can be given an additional poison counter. The player who proliferates chooses which player that is. See rule 810, “Two-Headed Giant Variant.” (CR 701.34). (Choose any number of permanents and/or players, then give each another
counterTo counter a spell or ability is to cancel it: remove it from the stack without resolving it. A counter on an object or player is instead a marker that changes characteristics or interacts with rules or abilities; for example, a +1/+1 counter modifies a creature’s power and toughness. (CR 701.6; 122.1) of each kind already there.)