Now, I want to start with saying that I don't like monks.

Anyhow, I was planning the party to encounter one of the BBGs, who happens to be an Arcane Archer. Currently it looks like out WoS monk we be the one to meet him first and he will be alone. Now the monk is level 5 and archer is two levels above him (he is not a world ending villain). Iam looking for a way to defeat the monk (I don't need to or want to kill him outright), I would however like an important character to not die to a single PC and considering waht monks do, that is really possible.

I should also mention that the monk is blind and is using blindsense and tremorsense to navigate around the battlefield.

If there is someone who can help, I would greatly appriciate it.

Simple, just don't let the NPC die. Going to zero HP doesn't mean that a character dies, just that they go unconcious.  You can rule that they automatically make the saves. We have enemies die automatically to fasttrack the NPC parts of combat.

Aside from that, there are any number of ways that you can allow for the NPC to escape, and many of them are commonly used to prevent PC total party kills (especially early in a campaign). If there is a narrative reason for the NPC to survive, then the NPC will survive. You could say that it was a body double, shapeshifter, or other similar option if you want the fight to go down to the wire naturally. You could have a creature capable of whatever type of resurrection is necessary. There could be some kind of escape hatch or a henchman could be ready to distract the monk.

The fact that the monk is blind means that they can't see anything outside of that blind sense range. The monk can still hear and smell, but there might be intermittent noises that distract the monk. A wash of water could carry the monk or NPC away. 

Quote from Warbaboon >>

Now, I want to start with saying that I don't like monks.

Anyhow, I was planning the party to encounter one of the BBGs, who happens to be an Arcane Archer. Currently it looks like out WoS monk we be the one to meet him first and he will be alone. Now the monk is level 5 and archer is two levels above him (he is not a world ending villain). Iam looking for a way to defeat the monk (I don't need to or want to kill him outright), I would however like an important character to not die to a single PC and considering waht monks do, that is really possible.

I should also mention that the monk is blind and is using blindsense and tremorsense to navigate around the battlefield.

If there is someone who can help, I would greatly appriciate it.

You have numerous house-rules in play which makes this challenging to answer - e.g. you haven't told us the range of the monk's blindsense or tremorsense.  You've also built an NPC using the PC rules, which is intrinsically bizarre by 5E standards (I seriously doubt the Archer's CR is high enough to warrant BBEG status).  In both cases more detail would be helpful.

Assuming you haven't been overly generous with your house rules and the Monk hasn't got the Alert feat, you'd basically have to go out of your way to have the Archer lose a fight like this - the monk sounds nearly entirely harmless.  Bear in mind the following (again, I am making assumptions because I have to):

1. The monk has no way to find the Archer, full stop.  Provided the Archer stays out of range of the tremorsense (which can be as easy as riding a giant owl or vulture), they can kite the monk indefinitely without being found.
2. Provided the Archer stays out of Blindsense range, they're functionally permanently invisible.  This is even more dangerous if the Monk lacks Alert.
   1. The monk is blind anyway, so the Archer's lair can be arbitrarily well-lit - it will help the Archer and won't help the monk.
3. The Archer can attack at least twice (more if you decide so), so the monk's 1d10+5+Dex damage reduction is hardly a show-stopper, and it's impossible for the monk's AC to be better than 19 at this level (assuming something like a custom mountain dwarf with optimized ASIs), so you can enchant the Archer's bow ahead of time as you see fit.

Quote from quindraco >>

 

1. The Archer can attack at least twice (more if you decide so), so the monk's 1d10+5+Dex damage reduction is hardly a show-stopper

Especially if the archer spams Grasping Arrow for the first three hits/rounds

Any archer in an elevated position versus someone who can't ever see them really isn't a fair fight

Have to agree with quin here, you're compounding the effects of two very problematic homebrew features: bad guys built as PCs and the good old "I want to be blind" PC. If there's still time, reconsider having those things in your game. If there's not, the monk should go down super easily as the archer can stay way back and shoot every shot with advantage. Drop the monk to 0 and then you're going to need to deus ex machina the situation with having someone else arrive or some other intervening force that keeps the bad guy from finishing him for good.

I'll skip past the advice that it's too late to implement. The deus ex machina that saves the Monk's life ought to be foreshadowed, at least. Maybe the fight is happening in an arena that's on unstable ground, like a collapsing stone bridge over a river. Then the Monk could fall in the river and get swept away. Or there's a nest of manticores nearby and the villain is trying not to wake them, but they wake up anyway and both parties need to flee. (I don't remember if some manticores would be a credible threat for a solo Monk at level 5 but you get the idea.)

Assuming the monk's Blindsense has a limited range of some kind, all the Arcane Archer needs is a Ring of Levitation or a pair of Winged Boots and suddenly the blind monk is a complete non-factor in their confrontation. If you want to avoid killing the monk then the archer doesn't even really need to fight them... just float away and mind his own business somewhere else.

Quote from TransmorpherDDS >>

Assuming the monk's Blindsense has a limited range of some kind, all the Arcane Archer needs is a Ring of Levitation or a pair of Winged Boots and suddenly the blind monk is a complete non-factor in their confrontation.

Heck, he could be sitting up in a tree, or up on a big rock. You don't need magic to make the blind/tremorsense combo useless

To be clear, unless the archer is hiding, the Monk can find his location (it's implied that he'd use his hearing or perhaps smell). So he can still target the archer with attacks, just at disadvantage. I'm not saying this isn't a considerable advantage, because it is. But it's not necessarily an automatic win.

And if the archer *is* hiding, then he's gotta beat the Monk's Perception, which is probably pretty good because Monks use Wisdom and have Perception as a class skill. And if the archer attacks, he's gotta hide again afterwards. And it takes an action. So... The archer can probably escape no problem (provided that he bails early enough -- he could get stun locked to death if he waits too long), but sneaky fighting isn't really the Fighter's strong suit. (I would still have him do this: hide, then attack, then hide, etc. Keep moving around. Even if it's a bad use of action economy, it makes sense and gives the Monk two problems to solve instead of just one.)

Quote from ChoirOfFire >>

To be clear, unless the archer is hiding, the Monk can find his location (it's implied that he'd use his hearing or perhaps smell). So he can still target the archer with attacks, just at disadvantage. I'm not saying this isn't a considerable advantage, because it is. But it's not necessarily an automatic win.

And if the archer *is* hiding, then he's gotta beat the Monk's Perception, which is probably pretty good because Monks use Wisdom and have Perception as a class skill. And if the archer attacks, he's gotta hide again afterwards. And it takes an action. So... The archer can probably escape no problem (provided that he bails early enough -- he could get stun locked to death if he waits too long), but sneaky fighting isn't really the Fighter's strong suit. (I would still have him do this: hide, then attack, then hide, etc. Keep moving around. Even if it's a bad use of action economy, it makes sense and gives the Monk two problems to solve instead of just one.)

 Even if the fighter is built like a PC, there isn't any reason that it needs to follow all of the rules that PCs do. Giving the fighter the ability to disengage or to hide as a bonus action isn't out of the realm of possibility and magic items do exist that could help out if you want to give bonuses tied to items instead of just by DM fiat. 

The WoS monk can cast darkness on the archer if they are within 60’ and not hidden, even if they only have 10-30’blind/tremor sense. And we have no idea where this confrontation will take place. So if it’s outside and wide open, the archer has the advantage. Inside or confined in some way the advantage diminishes. And the monk can put darkness on themselves and Hide which can bring the fight to a stalemate. If the archer gets to close the monk can shadow step up to them and stunning strike. 

So I don’t think it’s an open and shut case, there are too many variables to consider. But I would say the archer has the advantage of the DM wants them to. 

And if all else fails, before the archer dies, they teleport, or get teleported out by their “boss” or whoever the real BBEG is. They did say they were not the main villain b