Boreal Outrider

If you control multiple Boreal Outriders, each of their triggered abilities will trigger separately. A creature could enter the battlefield with multiple +1/+1 counters on it this way, even if you spent only a single snow mana of the appropriate color(s) to cast the creature spell.

The {S} symbol is a generic mana symbol. It represents a cost that can be paid by one mana that was produced by a snow source. That mana can be any color or colorless.

Unlike effects that care only whether or not you spent snow mana to cast a spell, Boreal Outrider cares about the color of that snow mana. It doesn’t matter which part of the total cost to cast the creature spell the snow mana was spent on, only that the spent snow mana matches one of the creature spell’s colors. For example, if a red creature spell has an additional cost to cast it and you spend red mana from a snow source to pay that cost, Boreal Outrider’s ability will trigger.