Bullywug Swamp Stalker

Amphibious. The bullywug can breathe air and water.

Speak with Frogs and Toads. The bullywug can communicate simple concepts to frogs and toads when it speaks in Bullywug.

Spellcasting. The bullywug is a 3rd-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 11, +3 to hit with spell attacks). It has the following ranger spells prepared:
1st level (3 slots): ensnaring strike, hunter's mark, zephyr strike

Standing Leap. The bullywug’s long jump is up to 20 feet and its high jump is up to 10 feet, with or without a running start.

Stealthy. On each of its turns, the bullywug can use a bonus action to take the Hide action. 

Swamp Camouflage. The bullywug has advantage on Dexterity (Stealth) checks made to hide in swampy terrain.

Swamp Strider. Moving through nonmagical difficult swampy terrain doesn't cost the bullywug extra movement.

Slay Foe (1/Turn). The bullywug deals an extra 4 (1d8) damage with its weapon attack if it hits a creature that doesn't have all its hit points.

Multiattack. The bullywug makes two melee attacks: one with its bite and one with its javelin.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) bludgeoning damage.

Javelin. Melee or Ranged Weapon Attack: +4 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 5 (1d6 + 2) piercing damage.