This has been mentioned a couple times in my streams and probably in the forum in the past, but I just want to bring attention to how annoying it is to count to 13 gems for any troops with that condition.
There should be some kind of effect around a card when they have their ability up and the 13 gem condition is on the board. This will save a lot of time on constantly having to count the number of gems on the board to see if it is indeed 13+.