Bogmaw Colossus

Amphibious. The Bogmaw Colossus can breath air and water

Aquatic Dominance. The Bogmaw Colossus's Devouring Vacuum becomes more powerful depending on its environment. While fully submerged, its vacuum has a range of 30 feet and pulls creatures up to 20 feet. While partially submerged or in shallow water, its vacuum has a range of 20 feet and pulls creatures up to 15 feet. While entirely on dry land, its vacuum has a range of 10 feet and pulls creatures up to 5 feet. The Bogmaw is considered fully submerged only when its mouth and throat chamber are underwater.

Internal Vulnerability. The Bogmaw Colossus has an Armor Class of 10 against attacks made by creatures swallowed by it. A swallowed creature doesn't have disadvantage on attack rolls against the Bogmaw solely because it is blinded or restrained. Damage dealt to the Bogmaw from within reduces its normal hit points.

Internal Rupture. If a creature swallowed by the Bogmaw Colossus deals 20 or more damage to it during a single turn, the Bogmaw suffers an additional 3d6 damage and must make a DC 15 Constitution saving throw. On a failed save, it regurgitates the swallowed creature into an unoccupied space within 10 feet of itself, where the creature lands prone. Internal Rupture can trigger only once per turn.

Catastrophic Rupture. If the Bogmaw Colossus is reduced to 0 hit points by damage dealt from inside its body, its abdomen ruptures violently. Any swallowed creatures are immediately expelled into unoccupied spaces within 10 feet of the Bogmaw and land prone. This rupture deals no additional damage. If the Bogmaw dies from external damage, its body collapses instead, and swallowed creatures can escape or be freed from its remains without taking further digestive damage.

Escape From Within. A creature swallowed by the Bogmaw Colossus can use its action to make a DC 17 Strength (Athletics) check, escaping into an unoccupied space within 10 feet of the Bogmaw on a success. A swallowed creature can also escape if the Bogmaw regurgitates it following an Internal Rupture, or through a magical effect capable of transporting it outside the Bogmaw, provided the effect's requirements are met.

Multiattack. The Bogmaw Colossus makes two attacks: one with its Crushing Maw and one with its Forked Tail Sweep. It can replace Crushing Maw attack with Engulfing Maw.

Crushing Maw. Melee Weapon Attack: +8 to hit, reach 10 ft,  1 target. Hit: 16 (2d10 + 5) bludgeoning damage. If the target(s) is large or smaller, it is grappled (escape DC 15). Until this grapple ends, the Bogmaw Can't use Crushing Maw against another creature. A willing creature can allow itself to be grappled, but the attack must still hit to deal damage. 
Forked Tail Sweep. Melee Weapon Attack: +8 to hit, reach 15 ft, one target. Hit: 14 (2d8 + 5) bludgeoning damage. If the target is large or smaller, it must succeed on a DC 15 Strength saving throw or be knocked prone. 
Engulfing Maw. The Bogmaw Colossus attempts to swallow one Large or smaller creature grappled by its Crushing Maw. The target must succeed on a DC 15 Strength saving throw or be swallowed. A creature can voluntarily fail this saving throw. A willing Medium or smaller creature within 10 feet of the Bogmaw can also allow itself to be swallowed immediately when the Bogmaw uses this action, without first being grappled. The Bogmaw can have only two creatures swallowed at a time. While swallowed, the creature is blinded and restrained, has total cover against attacks and effects originating outside the Bogmaw, and takes 7 (2d6) acid damage at the start of each of the Bogmaw's turns. The swallowed creature can attack the Bogmaw's internal tissues and use the escape methods described in its traits.

Devouring Vacuum. (Recharge 5–6). As a bonus action, the Bogmaw Colossus rapidly expands its throat chamber, creating a powerful suction current. Each creature of its choice within range that isn't behind total cover must succeed on a DC 15 Strength saving throw or be pulled directly toward the Bogmaw. The range and pull distance depend on its environment:

fully submerged, 30-foot range and 20-foot pull;

partially submerged or in shallow water, 20-foot range and 15-foot pull;

entirely on dry land, 10-foot range and 5-foot pull.

A creature stops in the nearest unoccupied space and cannot be pulled through solid obstacles. A successful save prevents the pull. This ability deals no damage and does not automatically grapple or swallow a creature.

Reaction Name. Enter the description for your action.