Leveling teams before a boss fight?

Hey just started playing im on the 2nd stratum and wanted to know if there was any easier way to level different pokemon prior to a boss fight outside of grinding?

I'm aware of thr level candy which is great but thst only gets you to the previous cap.

If theres some way to efficiently level so I can experiment with new teams prior to a boss that is what I am looking for.

Thanks!