DOUBLEBACK.
A multiplayer parkour shooter where you can rewind the last 4 seconds. Unreal Engine 5 — built by one designer and Claude, on a MacBook, in 6 days.
Own product · solo + AI · Steam Next Fest demo, Feb 2027
- What
- A 1v1 / 2v2 parkour shooter on a wet night-city avenue, built around one mechanic: rewind 4 seconds.
- Why
- To prove a single designer with AI can ship a real Unreal Engine 5 multiplayer game — not a mock-up.
- My role
- Head of design and director: mechanic, look, feel, every frame reviewed. Claude as the whole engineering and tech-art team.
- Result
- 6 days to a packaged, playable build · 3 heroes · server-validated rewind · demo planned for Steam Next Fest
Run, wall-run, take the hit — then doubleback four seconds and do it right.
Read the full story
Shooters punish one mistake with a death. DOUBLEBACK gives you one button to take it back: everything you did in the last four seconds rewinds — position, speed, health — and the you-from-the-past keeps running as a ghost. The hit you took becomes a feint.
The constraint was deliberate: no studio, no budget, a MacBook Pro M2 with 16 GB of memory. Big templates like Lyra don’t even fit in that memory, so the game was written from an empty C++ project — the rewind, the movement, the network code, the HUD, the bots.
Alex directed: references, mood, camera, how a jump should feel, which frames are wrong. Claude engineered, built the city from code, set up the lighting, retargeted the animations, wrote the tests and packaged the builds.
Four seconds. One button.
Press rewind — you snap back to where you were four seconds ago, and your echo replays what you did.
The rules that make it fair
- Exactly 4 seconds, no scrubbing — one button, one readable visual.
- Position and speed come back; health heals to the past value — rewind never hurts you. Ammo does not come back.
- History is wiped after a rewind — the next one needs four fresh seconds, so there is no ping-pong. 8-second cooldown.
- The server decides. The client sends a timestamp; the server takes the frame from its own 30 Hz history buffer, so a cheater can’t rewind to a place they never were.
- Echo strike: fire, then rewind within 1.5 s — the ghost repeats your shot from the old position. You spend an echo charge (up to 3, picked up as holograms on the map).
The street is the weapon.
Traffic drives at you, the avenue is wet, every bench, barrier and fire escape is a line to run.
Three runners, three rhythms.
Same rules, different feel: each hero tunes how long a wall-run lasts, how far a slide goes, how loud the steps are.
From a 3D scan-style model to a playable hero
Each hero started as a generated 3D model (Tripo), was rigged in Blender, and got animations from Mixamo through an IK retargeter — direct imports twisted the torso by 90° on pistol poses, so every clip goes through a proper retarget. The colours stay exactly as designed: heroes pop through light, not repaint.
Evening after the rain.
A wide avenue closed by a flatiron tower, a boulevard with crosswalks and traffic lights, a park with a pond, a roadworks zone to fight through — and a skyline instead of the void.
Built from code, not by hand
The arena is assembled by Python scripts inside the editor from Epic’s free City Sample buildings: a plan in metres, a footprint for every building, and rules — trees only in lawns with curbs, parking and a sidewalk for every building, crosswalks only at gaps in the boulevard, road paint 1 cm thick. Change a rule, rebuild the city in minutes. The same scripts place traffic, fire escapes with textured metal, roadworks with barriers you can vault and scaffolding you can climb.
Made for a gamepad.
Every action is one press. Combos come from timing, not from finger gymnastics.
Rewind
back 4 seconds
Signature dash
7 m, bullets pass through
Trick
flip or dodge with the stick
Quick aim
locks to the nearest target
Echo strike
your ghost repeats the shot
Dash into roll
within 0.35 s
Finisher
with a camera orbit
Trick-shot
×1.5 damage, perfect accuracy
A name you can play backwards.
The working title ECHO-SHIFT became DOUBLEBACK: a split magenta / cyan wordmark — the word itself turns back on its middle.
Six days, counted.
lines of C++
33 source files: movement, rewind, netcode, weapons, bots, HUD
Python scripts
6,899 lines that build the city, the light, the materials
history buffer
5 seconds per player, validated on the server
network test
host + client with 1% packet loss, run by script
retargeted clips
pistol, rifle, dodges — through an IK retargeter
heroes
one roster for the demo: Glitch, Data, Kira
A MacBook is not a game studio.
Every problem was measured before it was fixed.
- 116 GB of memoryNo Lyra, no big templates: an empty C++ project, one heavy process at a time.
- 2Twisted animationsMixamo clips imported directly rotated the torso 90°; an IK retarget fixed every pose.
- 3Frame rateA/B runs of the packaged build showed the city is fine — characters are the cost. Next: lighter models at distance.
Designer in the chair, AI on the tools.
One arena, three heroes, bots — a demo for Steam Next Fest in February 2027.
