Here’s the setup:
My familiar is adjacent to a target. My familiar is blinded.
I cast a touch spell. My familiar uses its reaction to deliver the spell.
Normally, being blinded causes you to attack at disadvantage, so I attack at disadvantage, right? I’m nearly certain about this, but wanted to confirm.
Casting while blinded in D&D 5e (mentions casting while blind, but not specifically the issue of a familiar delivering a touch spell)
Blinded + casting a spell with a bonus action + Find Familiar
Does an invisible familiar delivering a touch spell have advantage?