I can see how this may end up skewing the balance as they put themselves on 20ft pillars with magic swirling around for ranged attackers and narrow places with difficult/damaging terrain for defenders. What do you do to counteract this?
Bring it on. They'll have to come up with a good reason why such a place exists in the city, and how they'll sucker their target to show up there. If they can do that it'd make Snakejaw a more interesting place, and I'd be all for it. If I trust them enough to build the encounter, I trust them to make it fun -- and it would sure as heck be fun to sit on top of a 20' tall pillar while you mire your foe down below.
That's not to say it'd be like shooting fish in a barrel. The lieutenants were chosen for competence. In addition, the PCs are relatively high profile as almost the only non-dragonborn in the city. They may want to weigh anonymity into how public their ambush is. It'll probably be 20' tall pillars and hindering terrain
at night.
This brings up a great point. The point of this is to make
sure it isn't a fair fight. It'll be a fight where most advantages, except for the opponent, is something that the players can control. You don't want to negate that advantage! PCs have so many fight conditions out of their control that it's fun to give them the other side of the coin once in a while.
I gave the players a choice of which lieutenant to target:
- the guy in charge of recruiting illegal gladiators
- the guy in charge of collecting money
- the guy in charge of procuring and selling illegal stuff
- the guy in charge of buying off politicians
- or the guy in charge of the organization's religious adherence to Morgaire (the God of corrupted authority and villainous bureaucracy)