Crystals can eject crystalline mass from their bodies to block doorways or even lockdown small rooms for protection. Crystals may use this skill once per 7 long rests. 

Crystals are anaerobic, which allows them to stay underwater indefinitely but they cannot swim. Crystals walk under the water to get around at an extremely slow rate.

Crystals are mostly anaerobic creatures, Crystals suffer very little suffocation damage from inhaling smoke or submerged underwater.

While Crystals may be immune to small flames (eg. small campfire) large flames/flame spells may shatter crystalline armor.

Crystals take less pierce and cut damage but more blunt damage.

Crystals Thicc. Crystals naturally have a high Charisma stat due to them being THICC, SHINY and CHISELED.