After about two minutes of real deliberation, I finally figured out the problem. The problem is AT WILL SPELL-LIKE ABILITIES. There are thousands of ways to make even the monsters seem underrated with the current ratings. Consider a monster with the following list of SLAs:
Fly
Improved Inivisibility
Dimension Door
Wall of Force
Cone of Cold
Chain Lightning
Heal
Horrid Wilting
Meteor Swarm
Mordenkainen's Disjunction
If a monster can use all of these at 25th level at will, the CR modifier is +3.6875 . . . This combination, however, would make a monster all but invincible until the upper reaches of the ELH, making a paltry +3.6875 seem pretty dumb. Invincibility for a mere 4 levels?
Them being at will is what really makes this combination deadly, and that's for a monster using them, not PCs!
My possible solution is to simply remove At Will abilities altogether. Go by number of times per day only, and use that calculation to figure out everything. See? Problem solved. At will abilities are just too strong for ANYONE when they're the right abilities.
Fly
Improved Inivisibility
Dimension Door
Wall of Force
Cone of Cold
Chain Lightning
Heal
Horrid Wilting
Meteor Swarm
Mordenkainen's Disjunction
If a monster can use all of these at 25th level at will, the CR modifier is +3.6875 . . . This combination, however, would make a monster all but invincible until the upper reaches of the ELH, making a paltry +3.6875 seem pretty dumb. Invincibility for a mere 4 levels?
Them being at will is what really makes this combination deadly, and that's for a monster using them, not PCs!
My possible solution is to simply remove At Will abilities altogether. Go by number of times per day only, and use that calculation to figure out everything. See? Problem solved. At will abilities are just too strong for ANYONE when they're the right abilities.