Head to head

Clockwork Countdown

Clear the board from 1 to the bull, then your 501 leg starts on the spot. Every number you miss knocks points off your opponent's 501.

Mode
Players
Scoring
Cutthroat is the proper game: every number you miss comes off your opponent's 501. Easier puts your misses on your own score instead. No one starts their 501 below 121.
How to play Clockwork Countdown
Both players work through the board from 1 to 20 in order, then the bull to finish, same as Around the Board always worked: any ring of the number you need counts, so a single, double or treble of it all advance you.

The moment you hit the bull, your own 501 leg starts there and then, even if your opponent is still stuck on six. Standard 501 rules apply: double out, bust on a score that would leave one or take you below zero.

Every dart on the board that doesn't land on the number you need is added up, and that total comes off your opponent's starting 501 when they get there. Miss a lot and you hand them an easy leg. Go round clean and they face the full 501. Nobody starts below 121, so the finish is never a free win.

First to check out wins the whole match, whether or not the other player has even reached their own 501 leg yet.

Easier option: your misses come off your own starting 501 instead, so a rough run round the board gives you a shorter leg rather than your opponent.

A coin toss decides who throws first. The board is always scored dart by dart, since the game needs to know which number each dart landed on. Once you're in your 501 leg, you can switch between dart by dart and visit total at the start of any of your visits.
Coin toss
Heads, player 1 throws first. Tails, player 2 does.