Which slime attack are you having trouble with? There are some attacks that you will want to press the wrong button to avoid the slime effects so be sure to experiment. There are no true Game Overs so even if you lose a battle you can jump right back into it.
General tips for dealing with the 'Slimed' Peril would be to remember that Heatstroke can actually use her powers when slimed and while Bondgetta cannot, she can just use the 'Give In' struggle skill to remove it (and she IS able to use her powers in the 'f*cked' Peril)
Finally, feel free to use the 'DIFFICULTY CHANGE' Key Item to adjust the difficulty if the game feels too grindy for you.
Thank you for playing and I hope this helps you overcome your slimy obstacle! ;)