UNDERTALE: REVENGEANCE

Raiden falls into the Underground. Play UNDERTALE start to finish on any route (Neutral, Pacifist, True Pacifist or Genocide) as pixel-art Raiden, with METAL GEAR RISING: REVENGEANCE read from your own copy.

• Raiden in the Underground: Frisk is Raiden everywhere, from walking and wading to Toriel's hand across the spikes.
• Blade Mode: in a bullet phase, hold C to slow time, aim the cut with the arrows and press Z to slice bullets in two. Cut three or more at once for a Zandatsu that restores HP.
• Parry: tap Z just before a bullet hits.
• MGR boss themes that heat up: A Stranger I Remain (Toriel), Rules of Nature (Papyrus), The Stains of Time (Mad Dummy), The Only Thing I Know For Real (Undyne), Red Sun (Muffet), I'm My Own Master Now (Mettaton), Collective Consciousness (Asgore), Sam's duel theme (Genocide Sans) and It Has To Be This Way (Omega Flowey).
• Battle ranks: MGR-style S/A/B/C after every fight.
• Codec calls: Boris, Kevin, Courtney, Doktor and Sunny call 45 times, with their real MGR codec portraits. Nobody knows where Raiden is. The phone is a CODEC now.
• Raiden can't get a word in: the fall wrecked his voice synthesizer, so the team only hears static. Down here he keeps trying to talk, and Flowey, Toriel, Sans, Undyne, Alphys, Mettaton and Asgore talk right over him.
• Jack the Ripper: on the Genocide Route they call him Jack, Blade Mode turns into a red RIPPER MODE and ordinary battles play MGR combat music.
• Pacifist: spare everyone and the team starts seeing this world in a new light.
• True Pacifist: worried calls from the True Lab (Raiden's heart rate spikes at the first Amalgam, and Kevin realises Jack is really gone). Alphys geeks out over a real cyborg, Mettaton can't tell if you're a human or a strange robot, and Asriel says you don't look like the human he knew.
• You don't belong here: Sans and Omega Flowey both know Raiden fell in from another world, and Sans is harsher if you killed Papyrus.
• GAME OVER: MGR's own radio call ("Raiden? Raiden, respond!").
• Item descriptions from Raiden's point of view, and the game starts fullscreen.

Single player. Needs UNDERTALE and METAL GEAR RISING: REVENGEANCE (Steam, PC). Saves separately from your normal Undertale save. Nothing from either game is included: it's all read from your copies on first Play (about a minute).

MIT licence. Remixing allowed. Built with AI assistance (Claude).