Okay okay, I'll drop the snark.
Honestly, I think the spell is fine. I can see it being really helpful for giving Advantage to fallen allies who are making Death Saves, and for negating a critical hit 95% of the time. Using this spell to give Advantage on other stuff would be a waste, though, since there are far easier ways to accomplish that (I mean, the Help action is a thing.)
My biggest complaint is that forcing a reroll AND giving advantage just feels weird, since these two effects aren't usually part of the same spell. That's like having Magic Missile also increase someone else's movement rate, or Healing Word ALSO give the caster advantage on save throws. In my opinion it should do one or the other, not both.
And I write this every time the subject comes up: Advantage is overused in 5E. It should be a rare gift, not a foregone conclusion, so I'll always push back on anything that adds yet another way to get Advantage.
On the other hand:
- It doesn't scale up when using a higher-level spell slot.
- It spends the caster's Reaction, so Counterspell, Hellish Rebuke, readied actions, etc., will be off the table until their next turn.
- A Stealth check vs. the caster's Passive Perception will defeat it.
- Invisible/Ethereal opponents will defeat it.
- Blindness, Darkness, Obscuring Mist, etc. all defeat it.
- It can be Counterspelled/Dispelled but honestly, why would anybody bother?
So how would I fix it? I would leave it alone, and not call attention to it. Since it doesn't inflict or heal damage, my players will likely ignore it. On the off-chance that one of the players notices it, buried within the pages of a sourcebook on my bookshelf that I never bring to the table, I would run it as-written and let the player discover for themselves how weird and lackluster it is compared to other 1st-level spell options. Every time they cast this spell, they won't be casting Magic Missile, Healing Word, Shield...