Amber Robe

Gem robes are early magic armor for the shirt slot only, and the gem you happened to find decides how much magic damage you get out of it. Amber sits near the top of the pile, behind only the Diamond Robe, so if you are settling on one to actually wear this is a fine place to stop looking.

The headwear decides the build. Wizard Hat pushes critical strikes, Magic Hat hands you a larger mana pool instead. Take the mana if you keep running dry on a spell you like, take the crit if your mana is already comfortable. Legs are free either way, so wear whatever gives the most defense.

Any gem robe worn without a Wizard Hat makes Tim spawn far more often underground. That is the intended route to the hat: put the robe on, go dig, and wait for him to show up.