Sensible approach to taking a town as a mini-BBEG

[Unoriginal]

Hey guys,
It’s more a theory crafting, then an actual question, but it will help me greatly in shaping encounters in next chapter of my campaign. In this case, we have a lizard folk shaman, leading a rather strong army with a goal of taking a rather remote human settlement. The objective is complete occupation of mentioned town, casualties among the townsfolk are not really an issue.

Shaman assets:

Minibosses:

• 5x Archmage (spell slots up to lvl 8),
• 1x Ancient green dragon
• 2x adult green dragon

Stronger individual mosnters:

• 10 x goristo
• 1x Nalfeshnee,
• 4x Hydra,
• 7x storm giant
• 6x giant constrictor snake,
• 2x medusa,
• 2x tyrranosaurus rex,
• 3x spirit naga,
• 10x giant crocodiles,
• 8x black abishai
• 10x basilisk,
• 10x giant lizard

Mobs:
Cca 500 lizardfolk warriors
All monsters are refluffed as lizard-fluffed monsters (dragons = poison flying snakes, goristos = “ram lizards”…)

This may seem as a sure win for the attackers, but the town they are attacking is also not without defences:

• Small town of about 3000 inhabitants, placed upon a sparsely-used trade route
• About a mile of clearing around the town
• Town is placed next to a river, about 50 ft wide

Town defences:
- 20 ft deep, 15 ft wide, flooded moat
- 20 ft high stone wall with towers
- A minor, sturdy stone fort in town

Militia:

• Given, this is sort of “wild west”, all adult males and a number of females are regularly training with simple weapons. Fully mobilized, militia counts about 900 commoners with simple weapons plus cca 50 level 2-3 fighters and some similar level casters
• At all times, due to travel, there are 2+1d3 adventuring parties present in town of average lvl 5
• There is a good chance of a stronger party visiting town too, so one more party of lvl 10
• With all counted defences, for an example Ancient green dragon is suddenly not much of a threat. He can do damage and scare a lot of people, but volleys of arrows will still be a pain. Manned walls are a problem (expected massive losses of attackers). Goristos may break down the gates, but this again means invading forces suffering greatly due to fire from rooftops.
• Also, there is no time for a long siege. Crows/sending stones and a potential adventurer with teleport may bring an army here fast, so it must be done fast.

How would you approach taking such town with these assets?

Thanks!

5 Archmages means 5 uses of Teleport, bringing 40 individuals with them.

Get a spy to bring 5 bits of the town, preferrably of the places that are important to take out first (alarm system, whoever is in charge in time of conflict, arseenal, the places where adventurers gather, the main gate, etc).

Before the town realizes the time to fight is right now and not in 2h, take :

Archmage 1:
-the Ancient Dragon
- the Adult Dragons
-the Medusas
-3x Black Abishais (acting as bodyguatds for the Medusas and the Archmage)

Archmage 2:
-the Hydras
-the T-Rexes
-the Nalfeshnee
-1x Black Abishai (acting as bodyguard for the Archmage)

Archmage 3:
-the Frost Giants
-1x Spirit Nagas

Archmage 4:
-2x Spirit Nagas
-1x Black Abishai
-5x Goristo

Archmage 5:
-4x Black Abishais
-4x Goristo

And have each group Teleport in the town at the relevant tactical points, at the same time.

This will cause massive initial damages, a lot of panic and morale loss, and cripple the defense as its key elements are annihilated in one swoop.

Things like arrow fire won't be as much of an issue because the defenders will be spread and have troubles hitting on enemies who are already in the streets.

Archmage 1, the dragons and the others are here to disable the biggest threats, be it the stronger defenders, those who are the best at keeping the population focused on defending, or those who can call for help.

Archmage 2, with the Nalphenees and the big meatbag monsters are here to target civilians/the most vulnerable combatants in large quantities. Their goal is to, purely and simply, slaughter people that the stronger defenders will want to defend, either forcing the town commanders to divert a lot of people from protecting tactical assets to do that or further demolarizing the defenders (and probably causing quite a few militia members to ababdon their posts in hope of saving the helpless targets). It's important to put the Hydras and the T-Rexes here, because in an open field they are obvious targets for the defenders, while inside the town massacring the defenseless they are pure nightmare.

Archmage 3 and the Frost Giants would probably be best to deal with town spellcasters or the non-critically-powerful adventurers.

And the two remaining Archmages with the Goristos are here to damage the gates or buildings that need to be broken.

Once enough damage has been done, the Archmages Teleport back to the army, everyone who can get healed is healed to full while the rest of the army marches on the town.

Something to remember is that the assault plan is likely to come from the Shaman. Lizardfolks don't feel the same way humans or even dragons do, but a Shaman competent enough to gather such an army probably is more than smart and wise enough to know how to exploit other humanoid species' feelings.

It should also be noted that as a Shaman, he probably has more experience leading in peace time than against enemies. As a result, making mistakes like:

-Cornering the enemies without an escape route, causing them to fight to the last.

- Committing obvious attrocities without realizing it will get some people to stand and fight against impossible odds just to spare their allies this fate or out of anger and indignation.

- Not realizing killing everyone isn't needed when they're fleeing and giving him victory, causing troops to be dedicated to wasteful pursuits

- Not realizing that not all his followers are willing to die for him and his cause all the time, resulting in him demanding a lot out of them without taking his troops' morale into account.

Can be expected (though not all of them, and certainly not all at once, if the Shaman is smart, wise and/or charismatic)