Metal Monarch

The Metal Monarch is a Hard Mode miniboss that can spawn in place of any Slime after Hard Mode with a 1/300 chance or be summoned with the Mechanical Slime. It behaves similarly to the King Slime, but is a lot deadlier.

Stats

 * 6000
 * 25 Defense
 * 50 attack power
 * 70 laser power
 * 40 slimethrower power
 * 10 defense (third stage, flying)
 * 20 defense (third stage, grounded)

First stage
In the first stage, the Metal Monarch will reflect magic, bullets and arrows, while also having 9999 defense. It is only vulnerable to attacks when it opens its shell to shoot one to three lasers at the player. It will bounce around on four large springs.

Second stage
When the Metal Monarch reaches 4000, it will unlock its second stage. Its springs will fall off now, and a rocket engine will appear, keeping the Monarch above the player most of the time. In addition, it will gain a new attack: a slimy flamethrower that inflicts Slow and On Fire for 20 seconds. It will also gain more lasers and lose its invincibility.

Third stage
When the Metal Monarch reaches 2000, it will split into two. One stays on the ground and shoots with its laser guns, while the other starts flying and shoots the flamethrower. Each has 1000.

Fourth stage
In the fourth stage, which is unlocked when one of the two Metal Monarchs die, the remaining Monarch will get a rocket booster, laser guns and a homing missile launcher if it doesn't already have them. In addition, the Monarch will appear to be on fire.

Once the Monarch dies, it will explode with the power of Dynamite, harming characters and tiles in the vicinity.

Drops
Only one of the following will drop
 * 3-5 (100%)
 * 100-140 Magnetic Gel (100%)
 * Metal Monarch Mask (10%)
 * Metal Monarch Trophy (10%)
 * Slimethrower (50%)
 * Rocket Engine (50%)

Credits
Credit for this idea goes to FlamingFirehound. Page creation goes to 652Graystripe.