Amphibious. The behemoth can breathe air and water. Freedom of Movement. The behemoth ignores difficult terrain, and magical effects can't reduce its speed or cause it to be restrained. It can spend 5 feet of movement to escape from nonmagical restraints or being grappled. Siege Monster. The behemoth deals double damage to objects and structures. Swipe. If the behemoth hasn't moved this turn, it can use its bonus action to make a Swip attack. When it does, its speed is 0 until the end of its turn. Feral Rage. While the behemoth isn't controlled by its creator, it makes all its attacks at advantage, but all attacks against it have advantage. Additionally, it can Dash or make a Strike attack as a bonus action on each of its turns. Frightful Presence. Each creature of the behemoth's choice that is within 120 feet of the behemoth and aware of it must succeed on a DC 19 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to this effect for the next 24 hours.
Multiattack. The behemoth makes one Strike and one Stomp attack. Strike. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. HitL 28 ( 4d8+10 ) bludgeoning, piercing, or slashing damage (your choice). The behemoth can choose to halve the attack's damage to also grapple the target (escape DC 19), provided it is Huge or smaller. A target grappled this way is also restrained. Only one creature can be grappled this way at a time. Stomp. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 23 ( 2d12+10 ) bludgeoning damage. Hit or miss, all other creatures within 10 feet of the target must make a DC 19 Dexterity saving throw, taking 2d12 bludgeoning damage on a failed save, or half as much on a successful one. Additionally, structures in that area automatically take the damage. Swipe. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 19 ( 2d8+10 ) bludgeoning damage. Until the start of its next turn, attacks against the behemoth do not benefit from flanking bonuses. Burst (Recharge 6). The behemoth sends out a burst of acid, frost, fire, shrapnel, or thunder in a 60-foot cone. Creatures in that area must make a DC 19 Dexterity saving throw. On a failed save, a creature takes 5d8 acid, cold, fire, piercing, or thunder damage (choose one when you create the behemoth). A creature takes half as much damage on a successful save. Depending on the damage you choose, additional effects occur as below.