I've been doing a lot of playtesting for Neapolitan, adding scenarios and testing new Assistants. After PlayCon I quickly added the third scenario and Clara illustrated a new assistant for me, and I immediately knew what abilities I was going to give the assistant because I've been cheating in my playtesting for months now.

In Neapolitan there's a moment in the mid-game where some of the more obvious pipes are laid down and you need to start thinking about how to place your remaining pipes so that all the customers get the right ingredients.

It really helps to lay out "temporary" cards showing bends or straight pipes to work out which pipes should go where, and what options you have. I've always used the backs of random old cards and drawn dotted lines on them to work out what's possible and what's not. And when I playtested, I always treated it like this was a $4 assistant.
With my third assistant I've finally made that official.

This lets me plot out my next moves, revealing that I've already messed up the Strawberry customer, but the Neapolitan, Strawberries&Cream, and Strawberry Choc customers are still a possibility for getting a tip.

The thing I'm wondering most now is: should this assistant be available from the very first scenario? My worry is that it's the kind of thing where you have to have played a little bit before you become aware of the "mid-game crisis". I'd rather introduce it when the players most appreciate it.