Graveheart

An entirely respectable experiment.
Britain, the 1980s. At a Scottish research facility, two scientists connect William Wallace’s skull, sword and shield to an experimental machine. Their aim is to make history. Their funding application is deliberately vague.

The Scottish research facility exploding at night
Results were immediate.
One entirely preventable explosion later, the facility is gone, both scientists are dead, and William Wallace is alive. A disappointing exchange of expertise.

Undead William Wallace in a graveyard, leading the invasion
He has taken independence rather personally.
Wallace and his undead army march south to liberate Scotland by invading England. The finer points are not open for discussion. His curse spreads to corpses, trees and military hardware. Even the trains are possessed, though this does little to explain the delays. Somehow, he has also kept all his hair.

The British colonel saluting with a pipe in his mouth
The man with the plan.
An ordinary British soldier standing in front of a Union Jack
The man being sent.
You were only supposed to rescue some reporters.
You’re an ordinary British soldier. Your colonel has sent you to retrieve the half-witted reporters from Crown Squawk News, who rushed behind enemy lines without protection.

Unfortunately, your guns are now cursed, your next weapon is no longer your decision, and the man leading the invasion considers defeat a brief administrative delay.

Command still expects the reporters back.

A retro FPS where William Wallace is back from the dead, Scotland is invading England, and your cursed weapons keep switching themselves at the worst possible moment.