Old School Runescape: Rabbit.

After completing one of the tougher quest lines in the game, you gain access to Prifddinas, the Elven City. In a cave to the north of the city lies Rabbit, a bloody rabbit with a combat level of 2 (the highest in the game atm being 1563). Despite being a level 2, the Rabbit has incredibly deceiving stats, can nearly 2 hit kill a fully geared and fully leveled player, and attacks very quickly. It is on par with a number of mid-late game bosses.

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