Alternate

Tabaxi and Yuan-Ti ambush

Here they meet two eldery Tabaxi hunters (Hooded Lantern and Copper Bell, use assassin stats) that introduce themselves by fighting a common foe. They provide vital foreshadowing on a number of topics, so take efforts to make this encounter go well, including fudging the defeat of the snake scouts if necessary.

Here is a malison scouting the city entrance in snake form. He's got a backup force of three groups of five purebloods led by another malison each. 

Either when the snake scout is discovered or when he triggers the ambush, the two Tabaxi start shooting snake people, helping the characters. At least one Yuan-Ti should burst into snakes each round. Even if their contribution won't ultimately matter, Copper Bell's ability should creep and awe the characters sufficiently.

Once the pesky snake people have been dispatched, the Tabaxi have the following to say:

1) We seek honorable death as hunters of the greatest prey.

• I, Hooded Lantern, am here for the King of Feathers. Prophecy tells it will be slain by a mighty warrior in single combat. I'd like to think I am that warrior. Either way, the King shall be the end of me.

• I, Copper Bell, am here for "the Night Snake". I have dreamt it will devour me, and have said farewell to my families to see if it is a true dream. Before that happens, however, I would like to find and use the great treasure, the Navel of the Moon, said to allow you to connect to your distant kin. 

(Feel free to play up their defaitism. And play up her promiscuous past, akin to hippie seventies free love, if you like! Nothing freaks out male humans as when you suggest their grandmother is sexually active) 

• Our friend and greatest hunter, Bag of Nails, have slipped into the clouds of the mind, and fears everyone is after him. He used to talk about the Navel of the Moon, but I think it is too late for Bag, who will soon be one with the ancestors himself. We have said our goodbyes. You must respect his mighty Oathbow; once he has set his sight on a prey none has lived. Should you encounter him and live to tell the tale, we ask only that you treat him and his body with respect. He was once our mightiest hunter, and does not deserve a pitiful death. 

2) the Yuan-Ti live mostly "across the water" where the palace is. There's quite a lot of them. Most of them worship undead and engage in grisly rituals, but not all of them. We have asked the snake people we have caught; their "king" is somebody called "Ras Nsi". Their "queen" (actually head priestess) is "Fenthaza". And the outcasts, that don't consort with the dead, are led by somebody they call "Kaas-bil".

3) there are images and temples to "old Omu gods" all over the city, that are neither praised Ubtao nor dark snake gods (=the nine trickster gods). We haven't really explored the city, though Bag has moved ahead.

4) We've seen two groups of paleskinned outsiders enter the city recently. First came a strange lot [reference description/picture of Argentate Blades, now caught/insane down the Fane] that were somewhat cordial, then an even stranger lot all dressed up the same and quite unfriendly they were too! It didn't take them long to make enemies with the snake people and boy did they like fireballs! [=Red Wizards, which will have arrived just a few days prior, and are still at large].

Hooded Lantern: replace Assassin poison with Hunter traits (+2d8 dmg against marked enemy bigger than Hooded Lantern). If you wish, make him have dim eyesight (which should make him get disadvantage, if that ever matters). 

Copper Bell: Also Assassin stats with a poison named "The Calling" (“something I learnt from the elves”), meaning her poison is one a) yuan-ti isn't immune against, and b) if it kills a human (half-orc, half-elf etc) or Yuan-Ti, a swarm of poison snakes bursts forth. 

K. Fallen Tree (original location #7)

Heh. You're gonna love this one. 

Bag of Nails is the greatest Tabaxi hunter that have ever lived. And he's completely nutters. Love his image - it's like a nightmare version of Disney's Prince John! Imagine describing to your characters hearing the whoosh of an arrow, and then see their faces fall when you say "it hits for 20d6 damage" not to mention "as you lose consciousness, you see your own name written on the arrow" 

He has divinatory powers that allow him to scribe the character's name on arrows, creating Arrows of Slaying three times per rest. He's ambushing them from across the river 600 ft away. He's even put up a dummy (location c) to draw the party's counterfire (which alerts the Yuan-Ti). He should come really close to one-shotting level 10 characters for that yummy fantasy frikking Vietnam experience 

I am planning to use a battlemap here, so characters can indicate where they go and where they look. With an abstract map, it's all to easy to say "I just hide, then I go around and take out the sniper from the back". It should be really difficult to target him, with his ability to move and re-hide after each shot. 

Of course, they're about 10th level, and he's alone with "only" 120 hp, so I'm sure they will handle him just fine. 

Hopefully they will still gain some respect for the greatest Tabaxi hunter that ever lived, and grant him a proper burial (together with the friends he killed  ) just as Copper Bell wished.

Bag of Nails: 120 hp, with "Oathbow"* (advantage at 600 ft range, +3d6 vs mark): one attack at +11 for 20d6 (my approximation = 1d8+3d6+6 dmg plus +4d6 sneak plus 6d10 piercing DC 17 Con save for half) or 40d6 on a critical :-) Arrows bear target's name (choose three PCs at random).

*) not exact DMG stats