You start with 100,000 gold and a Rusty Pocket Knife. Your gold is your score.
Upgrade to raise the weapon's tier, from +0 up to +25. Each upgrade costs gold, and every tier costs more and succeeds less often than the one before. Higher tiers also sell for much more. The panel under the weapon shows the cost, the chance of success and what happens if it fails.
When an upgrade fails: below +10 the weapon drops one tier. From +10 to +19 it either drops a tier or breaks. From +20 a failure always breaks it. A broken weapon is gone, and you start again from the Rusty Pocket Knife. The knife always upgrades and can't be sold.
Sell turns your weapon into gold and hands you a fresh knife.
The Shop sells Auto Upgrades, which give you a +10, +15 or +20 weapon straight away (your current weapon is traded in at its sell price), and Upgrade Charms. A charm saves your weapon from breaking once and is used up automatically on the next break. Auto Upgrades cost more than climbing there yourself on average. You pay for the time they save.
After 10 upgrades you can Submit. Your weapon is sold first and your gold becomes your final score. If you run out of gold with only the knife in hand, the game ends.
Keys: U or Space upgrade, S sell, B shop, Enter submit, M mute.
