I want to create a blind archmage villain, and I'm trying to find all the handicaps that his blinded condition would come with. My first impression is that "if you can see the target" spells are all out of the archmage's reach.
So my question is, What drawbacks does a blind spellcaster have?
I'm interested in RAW answers as well as rules interpretations.
GoodSirTheSir has a good response about the mechanics, but if this is something you really want to do then you can use RAW to make it work.
One of the biggest boons for this is that Advantage and Disadvantage do not stack, but instead cancel out.
Basic rules p. 57:
If circumstances cause a roll to have both advantage and disadvantage, you are considered to have neither of them, and you roll one d20. This is true even if multiple circumstances impose disadvantage and only one grants advantage or vice versa. In such a situation, you have neither advantage nor disadvantage.
If your spellcaster is blind, they will always have disadvantage on attacks. However, if they find a way to give themselves advantage on the attack (which is pretty easy in 5e with helping, spells, and DM fiat), then the disadvantage goes away and they're back to making regular attack rolls. They will never be able to get advantage on an attack, but spells like Bless can help make up for that. An additional bonus is that as long as they can give themselves advantage in some way, they will never ever be forced to roll attacks at disadvantage.
5e, in my opinion, has very strange rules for unseen attackers. Being unable to see someone seems to have no bearing on whether or not you are aware of their location. Furthermore, there is nothing that states that being unable to see someone has any negative effect on your combat efficacy at all. Other than failing checks that rely on sight (which, other than counting birds a mile away through a plate glass window is 100% up to interpretation and thus DM fiat), you can be blind as a bat and still have perfect situational awareness. In fact, there are some situations where it is easier to detect someone if you can't see them than if you can (passive perception vs active perception for hiding, using the 'Lucky' feat, etc).
Here are the rules for attacking unseen attackers:
When you attack a target that you can’t see, you have disadvantage on the attack roll. This is true whether you’re guessing the target’s location or you’re targeting a creature you can hear but not see.
This is a very important part. It states that you have disadvantage whether you're guessing the target's location, or whether you can hear but not see them. In your case, you can hear but not see the enemy, so by RAW you don't ever have to guess where they are. You just 'know' their location.
If the target isn’t in the location you targeted, you automatically miss, but the DM typically just says that the attack missed, not whether you guessed the target’s location correctly.
Again, the above rules state this only applies to when you have to guess at the target's location, which is not the case when you can hear the attacker.
So, as long as you can hear the attacker, you always know where they are.
The biggest downside I can determine is that if you're blind, anyone can hide from you at any time as a standard action. Basically, you're granting the enemies permanent invisibility:
An invisible creature can’t be seen, so it can always try to hide.
If you're facing smart enemies, they will realize this eventually and make stealth checks even when they're standing next to you. If you fail the perception check to detect them, they are now 'hidden', and according to the rules that means that you no longer know their location (and would thus be beholden to the 'attacking unseen targets' rule above).
So, if you concentrate on giving yourself advantage, and giving your enemies disadvantage, you'll have almost the same efficacy as if you were never blind in the first place.
Let the spellcaster be blind but give him a familiar that he can use to see through and deliver spells through.
He'd want to stay hidden since his defenses would be weak (per the Blinded condition) and the familiar might need to be beefed up (or give him multiple) to keep combat interesting.
However, as @KorvinStarmast hints at, if he had Blindsense, he might still be able to use touch spells in melee as well as helping him defend against melee attacks normally. Blindsense would be no help against ranged/area attacks though.
