As it is a mountain I didn't add ": add " should I ?

You can just use them as a regular mountain, etc or you can filter snow through them for CC. useful if this is your only source of Red mana and you nedd , but only in an emergency. This T1, say a Snow Plains T2 and you can use either or on T2 with the limitation that, if you use , you'll be down one mana on your following turn.

The way Wizards do it is for nonbasic lands with the basic land types, they give the inherent mana ability in reminder text:

> (: Add to your mana pool.)

See Madblind Mountain, Sapseep Forest, Dryad Arbor etc.

Personally I think it doesn't need to "doesn't untap" rider on the second ability, since it's already got ETBT to make it not better than a Snow-Covered Mountain. Perhaps if the ability was ", : Add " rather than ", : Add " that might be necessary, but when it's restrictive enough to require snow mana, I don't think you need to further discourage the ability.

I'm taking your advice on the reminder text and removing the "doesn't untap" rider on the second ability. I think you are right that with the restriction in the activation cost it's enough. Thanks for the feedback.