Crystal is the most survivability-focused mutant in the game. Being the only character with 10 HP, Crystal already has a defensive advantage. Additionally, Crystal can safely avoid most projectiles through the use of her active Crystal Shield. Her ease of use and extra health makes Crystal a great starting character.
Crystal can create a shield around herself which prevents damage. The shield can be sustained for a short duration and Crystal can't move when her shield is activated. The shield will start shaking before automatically deactivating. Crystal is vulnerable to damage during the shield's disappear animation. The ability can't be used again until the previous shield fully disappears. Enemies will act as if they have lost sight of Crystal when she is shielding, and closer enemies will get repelled.
Attacks deflected by the shield:
Common red projectiles such as those fired by Big Dog or Bandits,
Shotgun pellets such as those fired by Alligators or Mole Sarges,
I.D.P.D. blue bullets and Inspector's slug projectile,
Discs from the Disc Gun.
Attacks negated by the shield:
Green ovoid bullets such as those emitted by Scorpions or Ballguys,
Fire, including the blue fire emitted by Lil' Hunter,
Toxin from toxic barrels and Toxic Ballguys or your own weapon,
Green bullets and orbs fired by the Palace enemies.
Attacks that bypass the shield:
Melee strikes such as that employed by the Assassin,
Lasers fired by Laser Crystals,
Lightning fired by Lightning Crystals,
Explosions,
Contact damage (Though enemies act as if they have lost sight of Crystal when shielding and won't run directly at her. Closer enemies will get repelled).
Throne Butt
Crystal's Throne Butt elongates shielding time.
Ultra Mutations
Fortress
Adds 6 max HP. Crystal will instantly get healed for 6 HP. Can be stacked with Rhino Skin for a max of 20 HP.
with rhino skin*
Juggernaut
Enables slowed movement while shielding.
Very useful in bullethell situations because makes you able to escape that situation.
Bunker
Allows shooting while shielded. Shorter shield.
Good with thronebutt, which negates the "shorter shield" debuff.
Vengeful
All projectiles deflected by theshield home in on enemies.
Gameplay
Crystal can be considered the best starting character for a new player due to her survivability. Her health boost alongside her special ability helps withstand heavy fire, plus the shield's reflective properties allow the player to kill enemies without spending ammunition. Releasing the shield and activating it again in the right moments can make you invulnerable for long enough that you can survey the situation before running to safety, which can be really helpful in the third stage. Her teleportation ability with Throne Butt adds to this, as you can escape any danger by shielding and teleporting to a safe location.
Useful mutations:
Euphoria - grants slightly more time to put up a shield and, in turn, evade projectiles.
Gamma Guts - when combined with Throne Butt, lets you teleport straight into enemies susceptible to contact damage.
Rhino Skin - added to Crystal's already above-average HP, grants a higher maximum total than any other character.
Stress - a higher maximum HP means it is possible to reach a lower minimum percentage of HP remaining, in turn increasing the fire-rate increase cap to one unmatched except by Chicken at 0% HP.
Throne Butt - grants more maneuverability, due to longer shield duration going into the centre of the battlefield and shielding wil kill most enemies.
Trivia
Crystal's loading screen tip mentions "Family". Crystal came from the Crystal Caves and her family is still there, trapped in crystal form. Crystal is the only one that can still control her own body and has any memory of the time before the apocalypse.
Crystal's other loading screen tip mentions that "Crystal can handle this", which implies that she is confident of her abilities and stays motivated.
Prior to update #82, Crystal's shield remained active for much longer. It got replaced with a slightly smaller, snappier shield. At the same time, her Throne Butt changed to teleport her after shielding instead of before shielding.
