You will need two relics and only one orb in your satchel.
The relics:
Round Guard (you become invincible when reloading)
Bad Cheese (deals damage to all enemies when reloading)

Notes:
The orb cannot be Orboros, unless you have Well-Done Steak
You can use two orbs if you have the Ambidextionary (can discard an extra orb) relic

Simply put, just discard your orb constantly.
The enemies can only attack when you're reloading, and Round Guard negates that.
Bad Cheese allows you to fight back and deal damage back to the enemies.

No cheese? No problem? This may take longer, but these relics still guarantee a win against (almost) every enemy if you play your cards right.

Shrewd Scales/Dumb Bell: After reloading dozens of times, your orb(s) deal massive amounts of damage.
Refreshield: This requires other relics to be useful, like Cookie, but lets you trigger "on refresh" effects on command.
Well-Done Steak: With Round Guard and a damaging Orb in your deck, you can take a break and heal with no consequences whenever you want.