Here is a crazy idea: Permanent Equipement cards that turns your troop in a Battle Form.
So, basically, in chests, you could get a very very rare (between Mythic and Legendary value) card called « battle equipement ».
You can then « merge » that card with any troop of base-rarity Epic or lower to give it a permanent boost. No refound. No turn backs. Only 1 equipement per troop.
You open some chest and get the « Power necklace of Guzmor »
It says: give a troop the following Battle Form: +2 magic. At the start of each turn, enchant myself.
You decide to use it on your Wolf Night.
You lose your Power Necklace of Guzmor, and Wolf Knight becomes Wolf Night (battle form) and now and forever has +2 magic and is always enchanted.
You pull the very cool « Armor of the Juggernaut »
It gives +2 to all stats and impervious.
You use it on Tau.
Now you have Battle Form Tau, with more stats and Impervious.
1- Give some love to lower tier cards
2- add another degree of collectible for hardcore collectors
3- make each account/collection unique and varied, because maybe my Giant Spider is not exactly like your anymore.