As another newbie who's only just starting messing around with Mictlan, I can't offer definitive advice.

But a couple of things I noticed.

Mictlan units aren't very demanding in resources, so you can probably safely put lots of scales in Sloth to get more points for your Pretender.

There are a lot of affordable Holy units, with some interesting extra abilities (can fly when blessed, or turn into Jaguars when blessed). Might be worth trying a Pretender with one or more high-level magic paths to exploit the bless effects you get from them. You might be able to build up an army that's mostly Holy, and massively boost it that way.

Mark