Amphibious. The dragon can breath both air and water.

Multiattack. It may make two attacks: one with its bite and a second with its tail. The tail must have a different target than the bite.

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 18 (3d8 + 5) piercing damage and the target is grappled (escape DC 15). Until this grapple ends, the target is restrained and the dragon can't bite another target.

Swallow. The dragon makes one bite attack against a target it is grappling. If the attack hits, the target is swallowed, and the grapple ends. The swallowed target is blinded and restrained, it has total cover against attacks and other effects outside the frog, and it takes 17 (5d6) acid damage at the start of each of the dragon's turns. The dragon can have only one target swallowed at a time. If the dragon dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 5 feet of movement, exiting prone.

Tail. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 14 (2d8 + 5) bludgeoning damage and the target is knocked prone unless it makes a DC 15 Dexterity save.

Standing Leap. The dragon's long jump is up to 30 feet and its high jump is up to 15 feet, with or without a running start.

Explosive Breath (1/day). The dragon exhales a dense cloud of explosive gas and ignites a shockwave in a 15-foot cone. Each creature in the area must make a DC 15 Dexterity save, taking 35 (10d6) fire damage and being knocked prone on a failed save, or half damage without being knocked prone on a successful one.

Hungry Leap. If the dragon takes a dash action and jumps at least 15 feet as part of its movement it can choose to land on a space occupied by one or more creatures. Each of those creatures must make a DC 15 Strength save or be knocked prone and take 12 (2d6 + 5) bludgeoning damage. If successful the creature takes only half the damage, isn't knocked prone, and is pushed 5 feet out of the dragon's space into an unoccupied space of the creature's choice. If no unoccupied space is available the creature falls prone in the dragon's space. If any creatures fail the strength save and are knocked prone, the dragon may immediately make a bite attack as part of the leap. If the bit hits, it may attempt to swallow the creature as a bonus action.

Bog Ambush. Bog dragons like to ambush their prey and will burrow into the soft peat or mud and lie in wait. While burrowed the dragon gains advantage on stealth checks, all active perception checks to see it are made with disadvantage, and the dragon cannot move. If it moves, all advantages are immediately lost.