DOOM

Single-player only. Cheats can turn off achievements and some saves; use them on a spare save.

1. Let monsters fight each other. If an Imp's fireball hits a Baron, they will brawl, so stand where enemies shoot through each other.
2. The shotgun is your best friend for most of Episode 1. Fire from just outside an Imp's reach and the pellets do full damage.
3. Strafe-run diagonally. Holding forward and strafe together moves you faster than running straight, which is how speedrunners cross big rooms.
4. Rocket splash hurts you too. Never fire the rocket launcher at a monster standing right next to you.
5. The Cyberdemon and Spider Mastermind take no splash damage from rockets, so you must hit them directly.
6. Firing a gun wakes up every monster that can hear it. Punch or chainsaw quietly when you want to pick off rooms one by one.
7. A berserk pack makes your fists stronger for the rest of the level, and it can one-punch Imps and Zombies.
8. Use the automap (Tab) constantly. Odd gaps between rooms almost always hide secret areas.

Tap a secret to reveal it.

• DOOM's first episode was released as shareware on 10 December 1993, uploaded to a University of Wisconsin FTP server that buckled under the traffic.
• Its fiction began as a mash-up of Aliens and Evil Dead II.
• id released the source code in 1997, which is why DOOM now runs on everything from calculators to fridges.
• The game's .WAD file format let fans build their own maps, and the modding scene it created is still active today.
• The fourth episode, Thy Flesh Consumed, arrived in 1995 as part of The Ultimate Doom retail release.