How the arena works

The game: Paper.io, 4 players

You start with a 3×3 square of territory in one corner of a 40×40 board. Every tick, all four bots move one cell at the same time.

• Trails. Outside your territory you leave a trail behind you. Step back onto your own territory and the trail, plus everything it enclosed, becomes yours.
• Cutting. If anyone steps onto a trail, the trail's owner dies. That includes your own trail: crossing it kills you.
• Collisions. Two heads on the same cell: both die. Driving off the board: you die.
• Death. A dead player's territory and trail vanish immediately.
• Reversing (e.g. LEFT while moving RIGHT) is ignored; you keep going straight. Before your first move you face the centre of the board.
• End. After 300 ticks or when one player is left. Survivors rank by territory, then the eliminated rank by how long they lasted.
• Timeouts. get_move() has 1 second of wall-clock time per tick. Go over once and your bot is frozen for the rest of that game: it keeps driving straight. Crashes in get_move() also count as "keep going straight" (the error shows in your console).

Rounds, points and the finals

Each team starts with 100 points. Roughly every 20 minutes the admin opens a round: a menu of games appears, each seating four bots. You pick one game per round, keep editing until the round locks, and then every game is played with the code you had saved at lock time. Empty seats are filled by house bots, which never earn points.

Points are the currency and the ranking: you spend them to enter higher-stakes tables and you earn them by placing well. When regular rounds end, points decide the seeds for the bracketed finals (seed 1 is the leader). Finals matches are four-player; the top two from each match advance until one bot remains.

Entry fees are deducted when you join and refunded if you leave before the round locks. "Returns ×2" means the winner receives twice the stake back (net +1×).

Writing your bot

Define a class Bot with a get_move(self, state) method that returns "UP", "DOWN", "LEFT" or "RIGHT". __init__ runs once per game, so store memory on self. print() goes to your console. Plain Python 3 only (no pip packages); random, math, collections etc. are fine.

class Bot:
    name = "Lawnmower"

    def __init__(self):
        self.turns = 0

    def get_move(self, state):
        me = state.me
        for direction in state.legal_moves():
            r, c = state.next_cell(me.row, me.col, direction)
            if state.is_safe(r, c):
                return direction
        return "UP"

GameState reference

Player

Globals available without importing: DIRECTIONS, DELTAS (direction → (dr, dc)), OPPOSITE. Coordinates are (row, col); row 0 is the top, col 0 is the left. UP is row − 1.