Zombie Knight: Rare mob that spawns on full moon nights with horse/shield

The Zombie Knight is a rare hostile mob that rides a Zombie Horse (making them obtainable in survival), and wears full iron armor, with a sword & shield. 1 in 75 zombies will spawn as Zombie Knights during full moon nights, provided there's enough space. Also, they'll only spawn after players have played in that world for at least 500 minutes, to prevent it from overwhelming new players.

In Minecraft, you'll automatically block frontal attacks with shields when riding a horse. The same goes for the Zombie Knight, which'll always look & chase towards players when aggravated, even at a distance, to prevent cheesing it with arrows. Of course, axes disable shields, and piercing crossbows will work, making them useful. When the Zombie Horse is killed, the knight will then act like a normal zombie, it'll not try to sneak to activate its shield, and instead simply chase the player.

Of course, the real reward in this fight is the Zombie Horse mount, if you can kill the knight without killing the horse. Like the Skeleton Horse, you can use Zombie Horses to travel underwater without dismounting. Skeleton/Zombie Horses should have variance in their speed, jump, & health stats, just like normal horses. But they cannot equip horse armor.

The purpose of this mob is to make Zombie Horses obtainable, and to give players a bit more challenge later in the game. It'll also give more reasons to the moon phase mechanic, other than slime hunting!

Please feel free to use this idea without credit!