Diamond is Unbreakable

At first glance Joe Diamond seems like the perfect investigator, especially for solo play - he can fight stuff good; he can get clues good AND he gets a discounted "extra" card every turn. What CAN'T he do?! Oh. Willpower tests. Those things that can utterly screw you over if you can't pass them and comprise the majority of treacheries. Being Willpower 2 makes trying to pass the average test (usually 4) actually quite challenging, especially if you move beyond normal difficulty. Accordingly, first port of call for upgrades is often Brother Xavier and Police Badge for safe static buffs. Geared Up exchanges doing stuff on his first turn for making sure all his subsequent ones will be at maximum output, and there's technically a chance for him to play Fast hunches too. It also means he'll have more resources available to pump into Physical Training for WP tests! A bargain if you can rely on getting good value out of it most game, and with nine items plus mulligans this is a fairly safe bet. For his hunches Logical Reasoning, Evidence! and Shortcut are usually in the main deck because of their dual pitchable icons and lower cost but of course you can swap them around between games anyway to suit the scenario.

...and yes, that IS a JoJo reference.