How to encounter the Ruby Guardian?

[Herbie]

There is a quest that requires bringing a large ruby, I had one at the early stage (received after defeating Ruby Guardian) but for a long time I did not find any use of it, so I sold it. Now, for almost a week I've been re-entering the Everchange Caverns, checking all the parts of it, but the Ruby Guardian does not appear at all, no matter what I do. Do I have to do anything special to make it appear?

[Vanilla]

The Ruby Guardian spawns randomly in the Everchange Caverns, but I think it's pretty rare to come across. Another way you could get a large ruby (that might be a bit easier) is to farm in the Caves to Midnight Mountain.

vvv Taken from the Wiki (drop chances for the Large Ruby) vvv

Monster   Chance
Ruby Guardian   Low (15%-29%)
Kingdom of Elyssia - Cave to Midnight Mountain (Zone drop)   Extremely Low (< 5%)
Kingdom of Elyssia - Cave of Darkness (Zone drop)   Extremely Low (< 5%)
Kingdom of Elyssia - Cave to Midnight Mountain II (Zone drop)   Extremely Low (< 5%)

So you could just farm like... rockscales and bloodfangs. Either way you choose, gl! :P
(You might've already known this too, but just incase: If there's ever an item you're unsure about where to find, you can search it up in the item database. By coming to the Paw'D Website > Game Guide > Item Database)