The Mythril Slime was created during the 1.1 era by a group of scientists for use by the Slime Army.
As much of the S.A's funds were used for ammo and supplies for troops, the scientists were left with only a few
platinum coins. Combined with the fact that the S.A had given them an unreasonably short amount of time,
the end product was sloppy. The first version of Mythril Slime looked like a basic green slime that was
stretched in MS Paint and recolored green using the default color palette. It didn't even looked Mythril.
It wasn't mythril.
However, despite this artistic failure, the S.A were happy with the result and sent the Mythril Slime
into combat without prior testing. The Mythril Slime made it all the way to the target's location thanks to a team
of Slime scouts, but failed to defeat the target. The nameless Terrarian that the Mythril Slime was supposed to kill
grabbed his sword and swung it into the badly drawn blob, and it exploded violently.
The S.A deemed the project a failure and decided to abandon it to the scientists to let them do whatever
they want with it. Since they no longer had a deadline, the scientists work on it for as long as they wanted.
Mythril Slime version 2 was much better. This time, it was equipped with the ability to shoot cursed
flames and upon destruction, will explode into smaller slimes. The smaller slimes were stuffed with artificial
intelligence obtained from vanilla monsters. The sprites however, still sucked. This version of Mythril Slime
was never deployed by the S.A into combat, but it was said that one of the models had escaped and was destroyed
by another Terrarian.
When the 1.3 update came, another group of indie slime scientists and artists discovered the long abandoned blueprints for
the second version of Mythril Slime. On their free time, they decided to develop a new version that was much more artistically pleasing
and deadly. While this was their first time programming and spriting a boss, they eventually managed to pull it off, and thus Mythril Slime v3
Mythril Slime v3 was sold to the S.A by the indie scientists. While the Army was furious that a small group of slimes did a better
job than they did, they eventually accepted the deal. The team of scientists brought their prized creation before the Slime Army officials and
presented it, telling tales of how great and powerful it is. This got the officials excited, and they instructed the scientists to turn the mechanical
slime on, and do a live demonstration of the powers they claimed it to have.
And indeed, the officials were shocked, but not in a good way. For the second it's great mythril heart started pumping, the Slime
began displaying it's arsenal of mechanical weaponry at the officials. In seconds, the Slimes were bashed, splattered and burned by the Mythril
Slime gone haywire, and not having a kill code implemented, not even the scientists can stop it. All they could do, was to spend the last few
moments of their lives watching on in horror as their creation showered upon them a blazing Mythril Meteor Storm.
Immediately, word of the massacre arrived at the Slime Army Command Quarters, and a battalion of Slime Special Forces were dispatched
to the area. With their machine guns, they opened fire and pelted rounds upon rounds of ammunition into the Mythril Slime, which dealt little more
than making a small dent in it. Then, the Mythril Slime charged, and the only the lucky soldiers survived. Followed was a wave of grenades at the great
mechanical, which blasted it away but could not deal sufficient damage, and it was then when the Slimes realised that they were probably screwed.
In ultimatum, the Slime Army launched an air strike on the Mythril Slime, already smashing away one by one at the frantic Slime soldiers
proving to be not more than a distraction, and a few cluster munitions were rained down upon the Mythril Slime, exploding into a fusillade of lesser bombs.
The Mythril Slime(and everything around it) were subject to a field of explosions, and it's great metal form slumped down to the ground. But upon closer
inspection, the Slime was not dead: it was merely passed out. The Slime Army had to act quick while they had the chance, and in no time, gunships carried
the body of the Mythril Slime to a far, far away land where it wouldn't be able to pester them again.
And from then on, no mechanical slime was ever made again.
(Oh and the place they brought the Mythril Slime to just so happens to be your Terraria world, because lol RNG)