UBERhelp1
Viceroy
I'd say merging an additional key. If you notice, there's an extra blue rock on the one that goes into the 3 keys. Either that, or just merging in an extra blue gem.The Cheat Sheet got an update - it now discloses how certain objects on the playing field may be combined:
using a special full key on a drop plate will give 3 keys... it is not disclosed, how that special full key is produced: I guess you combine two full keys or it is generated on random when creaing a full key?