Can not be targeted by most things when burrowing (details up to DM discretion).

Bite / Headbutt. Melee Weapon Attack: +5 to hit, 10(2d6+3) Piercing or Bludgeoning damage (depending on attack variation)
If using 1*3 tiles for monster space (instead of standard large size), only the range counts from the head.

Tail Smack. Melee Weapon Attack: +5 to hit 4(1d6) Bludgeoning damage in a 5 tile wide arc (u shape around tail). Hit enemies are pushed back one tile perpendicular to the arc
If using 1*3 tiles for monster space (instead of standard large size), only the range counts from the tail tip.

Absorb Magic. Optional: Reaction to magic being cast within 60ft. It consumes the magic and nullifies the effects of casting.
Can not be used again until (5 turns have passed or) Raw Magic Pulse is triggered.

Raw Magic Pulse. Mandatory: reaction to being hit (in melee) if it has absorbed magic when last taking a turn. All characters within 60ft must roll either their casting ability or constitution as a saving throw DC 8, upon fail take 1d4 damage.
The spellslot is refunded if last magic absorbed was from a level spell.