I like the idea of using the extra tower and item cards but the problem is players will have a lot more potions now. Perhaps it should turn them common or uncommon.
It might be a good idea also to add some indicator that the cards are being transmuted when you swipe the first three up. As the effect is currently, it looks like you're destroying the card, rather than transmuting it. Then suddenly, when you 'destroy' the fourth card, WHAM! NEW CARD!
Other than that, the effect looks really nice.
Yes, I was wondering if some text like 1/4 or 2/4 would help. What I recognized when testing this on my phone was that when returning to the stash you no longer know how many cards are already transmuted.
Maybe a small 1/4 with next to a icon version of the "Transmutation Symbol" (that magic circle looking thing that goes around the rarity after a transmute) in the upper-right / upper-left corner of all cards for a given rarity?
So say you transmute 2 Commons and 1 Uncommon, it would show 2/4U at the top of all Common cards, and 1/4R at the top of all Uncommon cards (where U and R are the icon, tinted blue and yellow, respectively)
This is good feature. Although I'm new to game but i never knew that common cards can be transmuted. Thanks
Good call. When testing this feature extensively I came to the same conclusion :-)
The indicator will be similar to what you suggested!