Keen Hearing and Smell. The mastiff has advantage on Wisdom (Perception) checks that rely on hearing or smell.
Death Bite. The rottweiler can, on an attack that hits, add 2d8 necromantic damage to the attack. After doing this, the rottweiler must wait a round before attacking again.
Bite. Melee Weapon Attack: d20+5 to hit, reach 5 ft., one target. Hit: d6+3 piercing damage. If the target is a creature, it must succeed on a DC 13 Strength saving throw or be knocked prone.