Wasn't able to find this anywhere, looked up "Glup Frog" "Frogs timeless" "Lesser timeless" etc... And some people might not be aware of it.
On the south east side of the isle is a spot with frogs with only 1.4mil hp who I believe has 100% or close to possible chance to rewards you with 1x lesser charm per kill and 70-80% chance to drop other lesser charm.
Possible coins depends on gear, but anywhere from 30+ for a fresh dinged 90 to about 100 if decent gear in 10min