Going Under

Make sure to never miss an opportuninty of conversation with Tappi. When the Dialog bubble is blue, she assigns you a task for mentorship:

Task one: Buy an expresso machine from the Joblin cafe.
I used Rays credit card to buy it. Alternatively you can try luck and have Swomp steal it for you. It's difficult to get enough money and Coupon app in first dungeon level to buy it normally. It never appeared for me in later levels.

Task two: Complete 3 combats in a row without getting hurt.
Use ranged weapons, helpers, or Youtubed app to avoid getting hurt.

Task three: Defeat the huge Rockstar in Joblin.
A challenge room has the task icon (square with a tick in it) on the door. Beat the inhabitants.

Task four: Put out 5 fires with water.
Do it in Winkydink. The guns shoot water, there are fire extinguishers, and torches too.

Task five: Make 60 dollars off a single Styxcoin conversion.
In styxcoin you can get extra cryptocurrency from destroying pots and rocks. Do not miss single challenge. Save money and in B3 or B4 you can buy the cash.

Task six: Buy 3 Weapons in 1 Run.
There are 4 stores in each dungeon, each usually has weapon on shelf. Just buy it. Ray can help, so does Swomp.

Task seven: Open 12 delivery cubes in one dungeon run.
Swomp gives additional cubes, exploding cubes count too. Tippis delivery boxes are also good idea.

Task eight: Complete floor B3 without spending money.
You need to hold on your money on floors B1 and B2 as well. Use Swomp to steal items instead.

I found it easier to complete all these tasks before entering the rainbow dimensional portal in the middle for the "F" achievement. The dungeons get more difficult then.