It's one of the better Slay the Spire "spin-off"
Basically for this broken build you want at least:
1x Reload
1x Warning Shot
1-3x Double Tap
The rest you can fill with 3-4 movement cards and good defensive cards such as Dodge and Redirect
Having more than 1 reload is also good but you'll want to upgrade all of them. Otherwise you'll get unlucky with the Draw card and it'll give you the not upgraded reload instead