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?
ANNI23|Cheat Sheet
ANNI23|Converter
ANNI23|Energy can be collected from quests and incidents or for purchase. Use it to spawn new pieces on the board or to reset your board without a board completion reward.
ANNI23|Fire Key
ANNI23|Fire keys can be collected from putting fire pieces with fully merged keys into the converter or from daily challenges. Use them to open valuable chests!
ANNI23|Grand Prize progress can be collected from freeing locked pieces on the board and by opening chests.
ANNI23|Key Conversion
ANNI23|Reset Board
ANNI23|Reset the board if you are stuck or collect a board completion reward if you have freed all locked pieces from a board.
ANNI23|Select pieces with a fully merged key and send them to the converter. The piece will be removed from the board and you will gain the key. The higher the level of the piece the more keys you will gain.
ANNI23|Spawner
ANNI23|The Cheat Sheet contains all the merge rules at one glance, be sure to check it out if you need help!
ANNI23|Use Energy to spawn 1 new piece on the board. All pieces have a chance to spawn but the higher level pieces have a lower spawn chance compared to lower level pieces.
ANNI23|Water Key
ANNI23|Water keys can be collected from putting water pieces with fully merged keys into the converter or from daily challenges. Use them to open valuable chests!
ANNI23|Wind Key
ANNI23|Wind keys can be collected from putting wind pieces with fully merged keys into the converter or from daily challenges. Use them to open valuable chests!
ANNI23|You will get 1 key for every 10 pieces of the same color without a key, for every 4 pieces of the same color with a half key and for every piece of the same color with a fully merged key. Automatic conversion is inefficient, so be sure to continue and check the board again before you claim the board completion reward and reset your board!Seems like my second guess wasn't that far off back then
