Slimes can speak and read Common, and Abyssal

You may "Counter spell" any incoming attack heading towards you, or an ally up to 10 Feet away. Launch the spell back at the user initiating a Wisdom saving throw (11 or lower fails)

NOTE : Doing this will cost a bonus action on your next turn, along with taking a quarter of the damage that would  be dealt to the target of the attack.

P.S : If the attack successfully reflects back onto the user, they will take the full damage of their attack.

Can only be used Once Per Short Rest.

2x Weak to any Water

2x Weak to ONLY Fire and Ice SPELLS

Disadvantage for 2 Turns when hit with Ice SPELLS.

Due to your adaptable body, choose any ability score to increase by 2, and an extra DIFFERENT score by 1.

Resistance to Acid

Immunity to Lightning, Psychic and the both the Blinded and Deafened condition.

When rolling saving throws on being restrained or prone, roll with advantage.

In Combat : When disengaging, twist and around and potentially hit enemies around you. Both you and the enemy(s) roll your lowest ability score and if you roll higher roll 1d4. Armor is not taken into account.

Out of Combat : Slip through certain narrow passages, or more likely, through grates and things such as cell bars.

Since Slimes have no brains their Saving Throws on Wisdom are at a Disadvantage. Along with their Intelligence Ability Checks.