Ancient Graboid

Subterranean Hunter. This creature moves at 225ft per turn while under ground. all melee attacks have x2 disadvantage (two rolls, take the lowest after the original Roll-to-Hit), and any spells that require a Roll-to-Hit. Any spells that require the target to be seen also don't work. 

Vibro-Hunting. Graboids have no eyes, BUT using the spikes along their sides, they can both move at high speeds. This also gives them an Opportunity attack chance when ever the players/ NPCs make any form of vibration (Movement, striking the ground, loud sound - explosions).

Ram. The Graboid makes a ground breaching charged attack that deals 4d10 bludgeoning damage. 

grapple.  after breaching, the Graboid will grapple, and drag its prey down. Make a Strength Saving Throw to avoid being dragged down. either way, take 5d8 piercing damage and be knocked prone.  

Tongues. uses its long, serpent-like tongues to grab and "bite" prey 5d12 piercing damage and leaves the prey grappled 

Gives The Graboid an extra edge on the field.

Devour (Costs 1 Actions). The Worm breaches the earth, either coming up, or coming down upon the players, swallowing them whole. players must make a DEX save over 18 in order to not be swallowed. if eaten, you have 4 turns to escape the beast.