Iron Crypticle

This achievement requires you to collect all seven colored jewels. The ones you have are displayed at the bottom of your stats screen on the left. You will assuredly collect some amount of these during each run, but getting all seven can really come down to luck. I have seen some people mention going for this in Endless Mode, since it's endless and doesn't need money for anything. However, most people's experience is that it takes 20+ waves to get lucky with the drops, and that's not the easiest most casual thing to do in the world. I opted to go for this in a normal run, and when I actually tried for it, I got it on Floor 3 of a New Game run. You still unavoidably need to rely on luck to get drops, but you also need to prioritize buying jewels from shops too. It'll be harder to survive without buying all stat upgrades, but you hopefully shouldn't need to buy more than two or three jewels from shops, with the rest hopefully dropping naturally. You can definitely try for this on NG+ so that you have more rooms and time to collect all seven before completing a run too.