You can scale monsters using switches and variables (if you don't want to use a plugin)
Have a common event with the variable set to check the player level. Then if it is greater then 30 activate a switch.
The switch can do one of two things:
Connect with a troop event that will empower the enemy (adding max hp/abilities) to the troop (even have it kick back to another common event if you want to play out animations to show them powering up). Or it can reveal hidden enemies that are only able to be battled when the switch is active and hides the weaker enemies. <-- have not tested this
Or
Change the random encounters to be more powerful versions of the monsters you have set -up.
I have it set-up for two dungeons in my game to have this happen, with 3 versions of the same enemies that scales at levels 10/20/30 depending at what point the players encounter the dungeon since there is an open world.
Once it is setup- it just requires duplicating the map and changing the ways in to map based on the lvl switch.
If you are doing this a lot, it could become cumbersome...but is a quick solution for isolated area's.