The Wurm is made up of a heavily armoured head and medium armour body. Represent these with two different minis. When the head emerges the body will follow after it burrows back in. The body stays in place until the head emerges in a new place.
Immune to prone and hampered.
Attacks against the body that miss inflict 10 damage against the attacker.
Target swallowed by a high bite attack take 20 damage at the start of their turn, are blinded, grappled and dazed. The wurm has no armour from attacks made by swallowed targets.
- •Breach.
The head emerges anywhere, then all creatures in reach 1, 10 damage, 1 push and prone, DC 15 Str save for half damage and no prone.
- •Massive jaws.
The head moves 3, then, attacks reach 3, 1d20+20, on a roll of 15+ the target is swallowed.
- •Regurgitate (reaction).
A target who does 30+ damage in a turn is immediately pushed 6.
- •Submerge.
The head disappears and is replaced by the body.
150 HP. The wurm's hard casing has been shattered, it's driven into a frenzy. It loses armour where the last blow fell (body or head). Until it dies it can emerge and bite on the same action.
The wurm is dying. 110 damage and it dies. Until it does it goes into its death throes which threaten to swallow heroes into a thrashing whirpool of wurm and ground.
DM note: represent the body with a long arch. We're going for Loch Ness monster arched back vibes here. Regurgitation while underground is an interesting possibility that should be improvised.