Please add more card option filters to the deck builder.
It would be quite useful if you can sort cards for
  • type (range, tank, fighter, spells and so on)
  • special type (charged, deathwish, aura, "support cards" like froniter bradley, warcry, teamwork like the coon, healing like jesus, area damage like nathan, none like dogpoo and so on), even if some cards appear in multiple categories like mint-berry crunch
  • engery (1-7)
  • level (1-7)
  • rarity (common, rare, epic, legendary)

You could remove the dollars in the deck builder, because they aren't useful at all there and it would be enough space for more buttons.
And you can select multiple filter at once -> for example: all legendary ranged units on level 4 (this could include craig, medusa bebe, satan, ninjew, mintberry crunch, callgirl, mecha timmy)
The balance changes, new cards or getting a good card on a higher level are shifting the meta so often thats its very hard and time intensiv to keep track on build unique decks.
For example I get a mysterion to level 4 and want to build my deck around him, so I can easily find matching cards and the matching genre.

Also it would be nice to have a compare button for 2 cards. If you hit the button you can select 2 cards and then the two cards are shown side by side. Also a second tab for the attack, health, range values in a side to side comparison with the difference of the values would be great.

I think this would be a huge quality of life update!

If you think it wouldn't fit in the layout of the game, a website or second app called "south park deck builder" would be an easy alternative. Just connect your game to the second app and then you can edit your decks and it will be changed in the game too.