I'm glad you liked how the difficulty increased with each round! We weren't able to include an endless mode during the jam's time limit, but after you play through the game once, a new button unlocks on the main menu that lets you pick one mode to play until you either win or lose all your hearts. It's not exactly the same thing but could be close to what you're looking for. Our team will definitely consider an endless mode option in case we try to enhance SLUG MODE in the future or make a similar game!