There's a problem with the game Loot Clicker. Nijsse spoke a bit about it here. Its 100 points medal is absurd to be achieved. But that's not really the problem with it.
The game is glitched and it randomly erases your hard earned equipment, that is, erasing your progress. It makes it extremely hard to achieve the last medal with progress getting erased every once in a while. You can see some complains here. And as it says there, it's not related to the amount of loot, it just happens.
Since it erases the equipment, the special demon mouse upgrade is gone and the Geared Up achievement has been removed. It can't be bought again because it had already been bought. Conclusion: the game's glitch makes it impossible to get the last medal. You can't get all achievements. Bother reporting on the broken medals thread? I doubt they'll believe it. Heck, Plinko medals at least were possible.
When I started this game, I feared that it would be practically impossible to get the last the medal, but I still tried it out and whatnot... But it was really the phony glitched impossible game that I suspected it would be. Don't play it, have something much better instead and that actually works: Idle Evolution.