Maxperson
Morkus from Orkus
Not me. The game.To say that there is no mechanical force behind it is the understatement of this site.
An 8 intelligence caster per 5e RAW can cast 9th level spells!
The dude has the ability to cast the highest level spells IN THE GAME but is incapable of determining that a Dispel Magic will be useful in a particular scenario?
So, roleplay-wise what you're going for is, the caster has intricate spells at their disposal but must be roleplayed like I'm not even sure what because they wouldn't know when best to use a Fireball, a Teleport or an Anti-Magic Shield. That must make for exciting combats.
The game determined that 8 is below average for intelligence. The game determined that intelligence represents the ability to reason, recall, and mental acuity. The game determined for some silly reason that the same 8 int can cast 9th level spells.
I'm just pointing out what the game does.
