According to Croteam, they made their own engine S-Cape 3D (an early name of Serious Engine 1) they stated: "Money was not the reason, although we couldn't afford Doom engine at that time, but rather as most the key guys at that time were programmers, so we decided to do our own tech (2.5D engine in the beginning)."
In the Flesh was going to be a fast-paced first-person shooter in the vein of Doom. According to the list of features on Croteam's website, it would feature 20+ enemies, four regular bosses and one final boss, cutscenes, high-res textures for everything and the ability to dismember enemies.
Technically, In the Flesh would be using the S-Cape 3D Engine, the predecessor to the Serious Engine. It was planned that In the Flesh would be able to support colored lighting, environmental effects like fog and haze, destructible environments and enemies that can be dismembered. Model data from In the Flesh can be found in the Serious Sam 1 SDK. Model data dated from early 1998 to 1999, when In the Flesh became Serious Sam, can be found in the SDK, which can be easily interpreted as data from In The Flesh.
Early screenshots dated from May 1996 show In the Flesh taking place in Fierd Dreams, Nightmares, and Hell. Models for items such as sofas, chairs, tables, and a cross suggest that In The Flesh was going to feature many items scattered throughout the world, which are almost all absent in the final game.
Serious Sam, who in that time was called "fleshy guy" in the earliest phase, used the same player model like in Test 1 in late 1996/early 1997, and his look was the same as the Hilarious Harry multiplayer character.
Croteam stated that: "He was actually a second iteration. First early look was how it looks now, as per my original design. However, we got some user feedback, along with some team members dissatisfied with the look and the fact that red sneakers, blue jeans and white shirt were silly to them, so I agreed with the change to make it more "realistic". However, when we showed that new look in screenshots to fans, there was a lot of uproar and almost all demanded to revert it back to original look, as they said it had a character, compared to "realistic" one."
The first original player model had only 303 polygons.
In The Flesh became Serious Sam in 1998, then they changed the scenario to ancient worlds and planets. Roman Ribarić had a dream where he should rename the game Serious Sam, since the title should sound something like Duke Nukem'.
Serious Sam: The First Encounter managed to accomplish a good chunk of the items that Croteam set out to do with In the Flesh, such a large amount of enemies on screen while using graphic effects like fog and haze. Some of them were scrapped, but have reappeared in other Serious Sam games. The idea of dismembering enemies appeared in Serious Sam HD, while destructible environments appear in Serious Sam 3: BFE and I Hate Running Backwards.
- Fierd Dreams
All of the enemies in this list have model data in the Serious Sam 1 SDK, which is when Serious Sam: The First Encounter was called In The Flesh.
- Beheaded Bomber
- Beheaded Firecracker
- Beheaded Rocketeer
- Scythian Witch-Harpy (a test model for the Harpy dated June 22, 1998 can be found in the “Test” folder in the Models data part of the Serious Sam 1 SDK.)
- Ugh-Zan III
The weapons in "In The Flesh" were actually the same as in the Beta.
- 12 Gauge Pump-Action Shotgun
- Double Barrel Coach Gun
- Lava Rocks Gun
- Military Knife
- SBC Cannon
- Schofield .45
- M1A2 Thompson
- XL4-P 'Ghostbuster' Beam Gun
- XM214-A Minigun
- XOP Flamethrower
- XPML21 Rocket Launcher