Here is the full list of all 12 Shiner achievements.
See ending 2.
Beat Sharpnut, Hardened Thief while knowing 6 or fewer total attacks.
See ending 1.
Lose a fight with Skrimpo.
Beat Gresh.
Learn every attack.
Beat Ranch before they run out of Divine Body uses.
Beat Leodora before they run out of Counter uses.
Beat Wally without using Fireball.
Beat Wally.
Beat Bouncer.
Beat Gatekeeper.