I was playing Pandora mode against Riv3rbird.
I have a water elemental in play, from multiple turns ago.
I jump it closer to the opponent.
I played unbound evolution on the water elemental.
The unbound evolution turned my water elemental into a sturdy shell.
So instead of upgrading creature from a 4 faeria to a 6 faeria, it instead downgrades to 2 faeria.
The difference lost me the game since went from a creature that can attack to one that can’t and I lost tempo since I played a card, it cost me 2 faeria, and it lost me 2 faeria that I already played.
Could it be, that you reduced the water elementals cost to 0, before you played somehow? (Like drawing it from a destroyed Baron Thulgar or something?)
Orosei and unbound evolution will “upgrade” the card from it’s cost, that is displayed on the board, not from the original card cost. So playing it on (your own!) cost reduced cards is usually not a great idea.
If the cost wasn’t reduced, then yes, this is a bug.
Yes, I believe I did discount it before playing it. That is a weird mechanic, every other game I have played the discount is the pay the card, and not the cards actual value decreases.
It is intended to counter cost-reduction decks, or decks that play Aurora’s Creation (like good old Apex deck)
It sounds like your Water Elemental was indeed reduced in cost to 0 somehow - which would be intended functionality for a +2 transformation effect to result in a 2 cost creature.
If this was not the case, please let us know if you can reproduce it!