If you can reasonably incorporate a jump into an attack roll (you need 2 unused move to jump) you get advantage.
- •Big Ole Bat.
Move 8, then attack for 1d6+2
- •Swinging with Two Hands!
Move 2, then attack for 2d6+4.
- •Get in Here! (1+ 1/encounter hero's skipped).
Call 3 Rabbit Thugs into the room.
The King is Bloodied! He can move 4 when he decides to Swing with Two Hands!
The King is Dying! 20 more damage and he's dead! He immediately calls in his two most loyal allies (a Bunny Fire Mage and a Bunny Chain Whipper)! These loyal allies act immediately after The King until he is dead, then they flee.
The King of the Rabbits should be encountered after the heroes raid his bandit home base, which is ideally a large indoor space with many rooms. The rooms should be designed in a way where the heroes can circumvent combat - maybe by stealthing, releasing sleeping gas, or even just not going in that room. During the fight, the King will call in those skipped bandits with his "Get in Here!" ability.
When the King is in his Last Stand, he summons his two most loyal allies. Those allies should have also been in the dungeon, but they should have been out of the way. If the party dealt with them before the King, he simply doesn't get stronger during his last stand!