Your cube shape and dense form make you difficult to move. You have advantage on saves and checks against effects that would move you against your will or knock you prone.

Your creature type is “ooze.”

You cannot speak, but you can communicate telepathically with one creature at a time within 60ft. If the creature understands any language, it understands you. You understand common and undercommon, as well the languages

Genetically evolved for life underground, you are accustomed to darkness.  You can see in darkness up to 60 ft in shades of gray.

Reaching out with a pseudopod is second nature when creatures are near.  You know the cantrip Primal Savagery.  The reflexive nature of this action also lets you use the spell when making an attack of opportunity.  Constitution is your spellcasting ability when you use this feature.

Creatures grappled by you and creatures who attempt to grapple you or touch you must make a CON saving throw, with a DC of 10 + your proficiency bonus.  On a fail, the creature takes 1d4 acid damage for every three of your character levels, minimum 1.  A creature must make this save when it first touches you and at the beginning of each of its turns while it remains in contact.

Accustomed to absorbing anything left behind for nourishment, everything can be food.  You are immune to poison and the poisoned condition.

Your semi-transparent body can be hard to spot.  When standing still and not in direct sunlight, you have advantage on stealth checks to avoid being seen.