Actions

Armored Defense. The nodosaurus drops down on its belly. Until it stands up, it gains a +4 bonus to AC and has advantage on Strength and Constitution saving throws. While in this stance, the nodosaurus is prone, its speed is 0 and can't increase, it has disadvantage on Dexterity saving throws, it can't take reactions, and the only action it can take is a bonus action to stand up.   Tail. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 3) bludgeoning damage.

Reactions

Reactive Counter. If a creature within 5 feet of the nodosaurus hits it with a melee attack, the nodosaurus can use its reaction to make one tail attack against the attacking creature.