critical up skills

Are these guys worth anything to anyone or am I just wasting monster space.

In my opinion, critical skills are not in as much demand as others, but are still more valuable than slumber, venom, or preemptive strike.

You'll find buyers once in a while, and you will probably have a better chance of selling if they are stacked. Most likely high-level players looking to max out monsters.

Keep in mind the demand and price of skills is always changing depending on the current event or any new monsters that come out.

Hope this helps.