If they wanted to get a little more damage in, they'd Giant Growth before the attack
In general, a 2/2 flash creature is worth a little bit more than a Shock
Like most Magic: The Gathering cards, the value of Mountain depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (European Land Program)
Besides its obvious implications in Mardu EDH decks already built around attack triggers, in formats like Standard you can benefit from multiples of these
- 101 Dalmatians/Peter Pan (Amber & Emerald) OR - Moana/Scrooge McDuck (Ruby & Sapphire) While supplies last
A Nexus of Fate deck was my first thought as far as combo shells go since those decks were already playing Drawn from Dreams back in the previous Standard format