Introduction

EXPcalibur is an Arena Style CTF challenge that I authored for The InfoSecurity Challenge 2026 (TISC 2026). In this Survivors-like game, a lone knight fights a swarm of enemies that grows stronger every second. No player controls the knight. Instead, each team writes a bot, and the bot plays the game for the team.

The game

The knight starts in the middle of an arena. Defeated enemies usually drop gems, and the knight collects the gems for EXP. Each new level makes the knight stronger and fully heals it, and this is the only way to heal.

A run lasts up to 10 minutes, and bosses arrive at 2:30, 5:00, 7:30, and 9:00. The run ends early if the knight dies. Your score is the total EXP that the knight collects.

How the challenge worked

As a participant, you went through these steps:

1. You signed in to the challenge site with your team token from the CTF platform.
2. You downloaded the handout: a compiler, a local runner, a sample bot, and practice seeds.
3. You read the documentation pages, which explained the bot language, its functions, the rules, and the arena.
4. You wrote a bot in a small C-like language and compiled it to a .bin file.
5. You tested the bot on your own computer with the local runner.
6. You uploaded the .bin file, up to 64 KiB, with a cooldown between uploads.
7. The server played your bot on seven hidden seeds and kept the median run.
8. The leaderboard, the Hall of Clankers, ranked teams by EXP.

You could also play the game yourself in the Try Game (Unranked) mode, but those runs did not count.

You can still try the challenge on a Linux x86-64 computer with the handout and the documentation.