Rampage. When the gnoll reduces a creature to 0 hit points with a melee attack on its turn, the gnoll can take a bonus action to move up to half its speed and make a molten bite attack.

Abyssal Gnolls make two melee attack of its choice 

Molten Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 7 (2d4 + 3) fire damage.

Greatsword. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit:11 (2d8 + 3) piercing/slashing damage

Longbow. Ranged Weapon Attack: +5 to hit, range 150/600 ft., one target. Hit: 6 (1d8 + 2) piercing damage.