Ambush. If the target of a heart seeker bow is suprised or if the echidna has advantage on the attack roll. The attack deals an additional 14 (4d6) poison damage.

Natural Camouflage(3/day). using its action the echidna can become temporarily invisible shifting its scales to mimic the colors and patterns of its surroundings. The naga is under the affects of invisibility.

Multiattack. The echidna makes either two melee attacks with her death spear--or two ranged attacks with her heartseeker longbow.

Death Spear. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 12 (2d6 + 5) piercing damage plus 10 (3d6) necrotic damage.

Heartseeker Longbow. Ranged Weapon Attack: +10 to hit, range 150/600 ft., one target. Hit: 14 (2d8 + 5) piercing damage then must make a DC constitution saving throw. On a failure the target takes an additional 14 (4d6) poison damage and becomes poisoned. 

Hide. The echidna can attempt to hide as a bonus action.

Parry. The echidna can use its reaction to raise its AC by 3 when attacked in melee possibly causing the attack to miss.