Why is this very rare? This is the same as a second level spell. This is an ability available at level 3!

Because it lasts 1 hour and requires no concentration.

That’s still not a very rare like potion. Rare at best

DM's can make up their own rules remember. I use a formula to determine the value of any potion which is Spell Level^2*100+any materials expended. but in my campaigns they always function exactly like the spell does so concentration still applies, unless of course I just feel like not mentioning it if the Players are struggling to survive and I want them too... Players rarely complain when the GM cheats in their favor afterall...

Yeah, I think that for a Very Rare potion this should really be greater invisibility... after all a scroll of invisibility is only Uncommon.

I would rule that by RAW this doesn't eat up concentration since it doesn't specify that you gain the effects of the invisibility spell(unlike other similar potions) so it is its own thing. Still it's more of a rare quality item, though not a terrible one at that level(anyone can drink those so no spellcaster required unlike the scroll and doesn't eat concentration if you want to combo say haste and this for a speedy invisible rescue mission). Probably a bit better than Potion of Heroism in terms of rare potions.

Quote from Yselieg >>

Yeah, I think that for a Very Rare potion this should really be greater invisibility... after all a scroll of invisibility is only Uncommon.

And a scroll of invisibility requires concentration and can only be used by a character that is in a class with Invisibility on its spell list, and if your aren't of a level in that class to cast it (3rd for full casters, 5th for half casters, 7th for third casters), then you need to make a DC 12 spellcasting ability check or lose the scroll... With the possibility of a mishap if you use that variant rule...

This item isn't for combat; it's for stealth. It would arguably be worse if it emulated Greater Invisibility since its duration would then be 1 minute.

Quote from LegendOfZub >>

Quote from Yselieg >>

Yeah, I think that for a Very Rare potion this should really be greater invisibility... after all a scroll of invisibility is only Uncommon.

 

And a scroll of invisibility requires concentration and can only be used by a character that is in a class with Invisibility on its spell list, and if your aren't of a level in that class to cast it (3rd for full casters, 5th for half casters, 7th for third casters), then you need to make a DC 12 spellcasting ability check or lose the scroll... With the possibility of a mishap if you use that variant rule...

This item isn't for combat; it's for stealth. It would arguably be worse if it emulated Greater Invisibility since its duration would then be 1 minute.

 I appreciate your use of logic.

Does anyone know what happens when someone successfully attacks an invisible player character? I can't find rules on that.

Everyone is complaining about the rarity when I’m trying to figure out the weight :(

It specifies that casting a spell or attacking breaks the invisibility. If you want to go by the rules, then even the creature and its blood are still invisible as long as it's on them. Cantrips are considered spells, but they don't use a spell slot, so you can't cast a cantrip without breaking invisibility. 

Beyond that, if an npc was invisible like this, I would still give disadvantage to attacks made by players/allies, because it's still harder to track them down without being able to see exactly where they are in their space.

Quote from johnnytapp184 >>

Everyone is complaining about the rarity when I’m trying to figure out the weight :(

 I'd weigh it about the same weight as other potions. Those described as a pint would probably be one pound or heavier. 1 pint of water weighs 1 imperial pound, and the bottle adds weight.

I make most of mine smaller, because its crazy to me, for a character to guzzle down 16oz of potion while moving and possibly casting a spell. I keep my largest potions at .25 pounds, and 4 ounces.