Undead Fortitude. If damage reduces the zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the zombie drops to 1 hit point instead.
Multiattack. The chimera makes three attacks: one with its bite, one with its horns, and one with its claws. When its fire breath is available, it can use the breath in place of its bite or horns.
Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) piercing damage.
Horns. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 10 (1d12 + 4) bludgeoning damage.
Claws. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage.
Fire Breath (Recharge 5–6). The dragon head exhales fire in a 15--foot cone. Each creature in that area must make a DC 15 Dexterity saving throw, taking 31 (7d8) fire damage on a failed save, or half as much damage on a successful one.
Calculated all the numbers by taking a ratio of the Chimera's equal to the ratio between he Ogre and Zombie Ogre, then rounded.