Inspired by the old classic game, Frogger.

Primary mechanic: dodge obstacles and avoid falling into the acid pools.

Secondary mechanic: attack enemies by moving into them.  Also, move into treasure chests to collect gems from them.  

The two mechanics form a nice and simple synergy common to many traditional and modern Roguelikes.

Clear the enemies and collect all the gems to advance (progress).

You can get the gist of it in just 5-10 minutes.