One Rank Higher

All of them are in The Gallagio
Red at 80,55
Purple 58,49
Blue 66,29
Gold 66, 80

Red does fire rings that can be dodged
Purple is healing reduction
Blue Will silence people
Gold increases boss HP

Turn ins for each coin is in The Lucky Heart
Only 1 is required for the achievement. You turn them into the room right before the boss. I would recommend doing red if you want just the meta achievement.

Step by step guide for all the achievements in Glory of the Liberation of Undermine Raider: https://youtu.be/LotBGmWtn-o

There is actually a set of 4 achievements for this, the first one is the one needed for the Glory achievement.

There are chips lying around on the floor in the fancy casino area before the one-armed bandit room. Depending on the chip or chips picked up, you can activate one or more of the slot machines just before entering the boss room. Each coin gives it’s own unique additional mechanic to watch out for:
- Red at 80,55 - huge fire rings - avoid getting hit
- Blue at 66,29 - shock waves that can silence players in range
- Purple at 58,49 - 80% healing reduction to players close to the boss
- Gold at 66, 80 - increases the boss' HP.

You can deactivate a slot machine and activate another if you wish to change the added mechanic, and you can activate more than one slot machine to get the other achievements as well. The achievement tracker will mark the achievement as met at the beginning of the fight, defeat the boss to earn the achievement.

It's very much worth mentioning that the purple one isnt just any healing reduction, but a 80% healing reduction to players within 12 yards of the boss