Question

What are the chances of a purple Raid Den appearing?

Comments

J, can you copy and paste my comment here, since your hiding your answer deleted it from my view. Thanks.

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Every time that you clear out a set of raid dens, one purple raid appears. Every time you see raid dens in a location, no more will appear until you clear all the raids that are there. Every day, the placement of the raids changes, but there is still the same number of raids. After you clear all of the raids, a new set immediately spawns. One of the raids is always a purple den.
- GmaxWaluigi

Answer 1

Every time that you clear out a set of raid dens, one purple raid appears. Every time you see raid dens in a location, no more will appear until you clear all the raids that are there. Every day, the placement of the raids changes, but there is still the same number of raids. After you clear all of the raids, a new set immediately spawns. One of the raids is always a purple den.

If you are using a Wishing Piece, yes the chance is 10%.

Source: experience

Thanks J!