Avalanche Caller

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.

Snow isn’t a type of mana. If an effect says you may spend mana as though it were any type, you can’t pay for {S} using mana that wasn’t produced by a snow source.

In most cases, the land that becomes a creature will remain colorless. If another effect caused the land to have one or more colors, the resulting creature land will retain those colors.

A land that becomes a creature because of Avalanche Caller’s activated ability will retain any other supertypes, card types, subtypes, and abilities it had. In particular, it will be a snow creature land.

Some cards have additional effects for each {S} spent to cast them. You can cast these spells even if you don’t spend any snow mana to cast them; their additional effects simply won’t do anything.

The Kaldheim set doesn’t have any cards with mana costs that include {S}, but some previous sets do. If an effect says such a spell costs {1} less to cast, that reduction doesn’t apply to any {S} costs. This is also true for activated abilities that include {S} in their activation costs and effects that reduce those costs.

The activated ability doesn’t cause the target snow land to become tapped or untapped.

Snow is a supertype, not a card type. It has no rules meaning or function by itself, but spells and abilities may refer to it.