Making an NPC always crit fail?

Is there some way to edit an NPC so that when you click on its attack, it ALWAYS crit fails?  The best I can figure out to do is edit the attack bonus field to add "1d2". That way even though it still ALSO rolls a d20, half the time it'll roll a 1 on the added d2 and the result will be red (which is ultimately what I want regardless of what the actual attack total is).  I tried adding 1d1 but that always makes the result blue colored. I need red.  Thanks for any help! 

If you are somehow trying to hide this from the players, I would recommend simply hiding your rolls and then telling them that the enemy crit failed.  If you create this roll and it shows in their chat, they can mouseover the roll and it will show that it was a d2 rather than a d20.

No no, I WANT Them to see the NPC crit fail. I have heretofore always rolled my NPCs in view of the PCs, and it would be outright suspicious if I stopped for this one roll in which the NPC who is pretending to be on their side, intentionally breaks a bow string. And if the PCs are clever and mouseover the number to see something suspicious, all the better! But I want a glance for it to look like a legitimate crit fail.

It is... possible with math shenanigans, if you have access to the math from the roll post it here.  Though, I'd be very careful with.  It is kinda easy to use the same methods to create an auto crit success, which is why a lot of the math is handled in a way which prevents tampering (at least tampering that is not immediately obvious).

The next best solution I can think of is a macro: /me rolls a [[1d2+6]]. but that doesn't make an output that looks like the usual NPC actions. And half the time ir gives it a green (crit success) box, which WILL look weird to the players, and not in the way that serves the story. (Though again, something that might trigger the players' suspicions. I'm not worried, we've been playing for literally years now... if a player becomes suspicious of something they know it's because of something plot-related, and not because the GM is messing with them. And that's the case here... the NPC is being deceptive. If the PC gets suspicious, they know to have their character be suspicious and investigate the NPC.)

Which character sheet? If it is the D&D 5th Edition by Roll20 sheet, then you would need to build the NPC as a PC sheet, since the NPC lacks a crit range. Edit any attack that needs to always critical fail. In the crit range field, where it normally says "20", write in "21cf20" They will now need to roll a natural 21 to critically hit, and will fail on a 20 or less.

Note that if they mouse over, they will see the to-hit roll formula. This is unavoidable and undesirable. The Roll20 team has gone through great efforts to avoid being able to spoof rolls. But it should be good for casual use and would definitely trigger the suspicions you are talking about.

keithcurtis said: Note that if they mouse over, they will see the to-hit roll formula. This is unavoidable and undesirable. The Roll20 team has gone through great efforts to avoid being able to spoof rolls. But it should be good for casual use and would definitely trigger the suspicions you are talking about. Like I have been explaining, I'm perfectly A-OK with the players looking at the roll results. If they happen to, it's a metagame layer of suspicion they will have for that NPC. We've been playing LONG enough where if they see something hinky going on, it's not me the GM trying to cheat them, it's the NPC doing something shady, and a clue that they need to investigate the NPC.

keithcurtis said: Which character sheet? If it is the D&D 5th Edition by Roll20 sheet, then you would need to build the NPC as a PC sheet, since the NPC lacks a crit range. Edit any attack that needs to always critical fail. In the crit range field, where it normally says "20", write in "21cf20" They will now need to roll a natural 21 to critically hit, and will fail on a 20 or less. Thanks for the tip! Except... seems that makes a natural 20 = a crit fail (red number) but all other d20 results just a black number.

Ah, I used: 21cf<21 and that makes all rolls appear as a crit fail! Thanks for the tip!!