Hello I'm new to the whole 2d assets scene, and I'm writing this comment to know if these assets can be used as monsters on my game to be able to attack and be defeated.
are you asking license wise? then yes! do as you please. This work is licensed under CC BY-SA 4.0 
This means you are free to share and adapt, but have to credit me.
if you are asking for additional spritesheets. request them on my fiverr: https://de.fiverr.com/michael_jay_rov?up_rollout=true
xoxo uwu for liking my work <3
My bad. This one should work:
https://de.fiverr.com/michael_jay_rov/breed-your-2d-pixel-art-creatures