I greatly enjoyed this game, it is the first twist on the balatro style progression system I actively enjoyed (outside of Balatro), and think you have built a very solid foundation to be reiterated on in the final release!
In that vein, I would like to suggest 7 things which would make me enjoy the game even more:
1) More Challenges
The first 5 are great, its just a gameplay style & concept that leaves me wanting more. I immediately thought of 2 possible additions based on the Fat mechanic the game prompts you with every couple of rounds:
Sumo, where you have to balance an equal amount of your gains threshold and fat threshold to win each competition.
Eating Contest, where instead of building the muscles you are exclusively adding to the fat threshold of your character. Every few rounds you are offered the inverse punishment/deal of gaining muscle that you need to get rid of in order to continue building up fat
Addtionally, the T-Rex Card inspired a silly mode idea:
Dinosaur, all it does is swap out the human head and add a tail, which acts as a new muscle group
I could see all of these leading to many new cards being added, which may spark even further ideas for challenges! I have a few further ideas for competitions & individual cards but I don't want to eat up too much of your time!
2) Longer Competition Unlocks
I thought a way to add replayability would be unlocking a longer variant of each after completing them! It could be as simple as adding an extra 5, doubling, or even tripling the amount. Leading to much crazier proportions.
3) Non-Traditional Difficulty Setting
Since the competitions are categorized on difficulty, I thought of a way to add challenge without going the standard route of making the upgrades less accessible each difficulty;
So if Normal is the standard Back, Chest, Glutes, Arms, & Legs; A Hard Mode could divide some of the preexisting muscles into multiple sections. Splitting the Chest into Abs & Pecs, the individual Arms, and Legs into Calves, Thighs, & Hips.
I figured this would add to the comedic sizing while providing with some greater challenge, in there being 9 muscles to work on instead of 5.
Perhaps cards specially made for those groupings could even work in standard gameplay, just offering half the effect. So a card that offers 6 Thigh Gains in Hard would be 3 Leg Gains in Easy.
4) Greater Customization Options
As a Gay Trans Woman playing this, I would really like to play as a woman if possible! I know cloth physics would not mesh well with a game like this; But if there was face & haircut customization, even if they were just presets, it could be fun to customize! Maybe unlockable hats as a cosmetic, so they dont have to scale with the player? And lastly could you let us pick any color for the skin? I think it would be fun to be a big blue or green giant.
5) The Artwork
I was just curious if you are still looking for an artist or artists to collaborate with on Card Art? If you would be okay with a slightly cartoon-ish style, I would happily offer my services!
This could also add a further layer of customization, with cards having different artwork to change between? Or atleast different art than the base when upgrading a card!
6) Sandbox or Endless Mode
This is mostly a by-product of Balatro letting you play until the program literally cant process a higher score maximum; But I think something fun you could unlock after beating all the modes, or maybe for each after beating their hard mode if you go for that idea, is just going as long as you can. The idea of seeing how Kaiju-esque these bodybuilders can get sounds terribly funny.
7) A Single Gameplay Tweak I Would Appreciate
Lastly, if this one thing could be changed during gameplay I would be really happy. I have a bad memory, and I would greatly appreciate if Upgrade packs could stop being offered in the shop if you have nothing currently to upgrade. I found myself buying them, fairly certain I had something to upgrade, only to realize I just lost out on $5 I could've gotten residuals on.
Thank you if read and double thank you if you like any of these suggestions! I have wishlisted and eagerly await for its release on Steam! ^_^