This section will contain stuff like funny/unusual things that happened during attempting the levels, trick demos showing things which won't be used in speedruns, or a different kind of run through the levels.
You need game version 1.05 to play the demos.

Demo - Backpack spawn kill

This happened to me during an attempt of the level Dunes on Tourist. Grabbing the Backpack at the end triggers the Kleers to spawn which are needed to get pushed through the door, but apparently I jumped in that spot at the exact moment it spawned and thus it killed me (Which I believe is known as a "telefrag"). I was quite surprised myself when it happened.
A similar thing also happened to me once when we were cooping Sierra de Chiapas from TSE, but then it was a Health Pill that killed me instead :D

Demo - Drunken Sam

A funny thing to simulate a kind of drunken mode. To make it work, all you have to do is crouch out of any water (Or if you need to jump out of water because there's no slope, jump and then press and hold crouch and land on the ground, but this method is a little bit more tricky).
Your view will start swaying like it does when you're underwater. In this "mode" you won't shoot exactly where your crosshair points to since your crosshair is moving around but the actual firing point is still in the middle of the screen making it somewhat more confusing to shoot at something ;)
Also, if you jump and just land on the ground, your view will be reset to normal. In order to keep the drunken mode, jump and then press and hold crouch until you've landed on the ground.
This works at any water place. This also works in The Second Encounter, but as far as I've tested it doesn't work in Serious Sam 2.

Demo - Metropolis done Knifed

Just a little something I threw together. The "big-bada-boom" is funny, and it's quite tricky to get on the wall as you can see.
Surviving the Kamikaze part without getting on the wall is difficult, if not impossible because those guys keep on spawning and you can't dodge them. You could maybe survive by hiding behind the wall at the front door, taking a peek to attract some Kamikazes and then take them out and hide again to restore health but... meh. The method I use is funnier ;)
This was done on Tourist by the way.

Link - A walkthrough of Serious Sam TFE (Xbox)

I came across a walkthrough for Serious Sam TFE on the Xbox done by Elbryan42. He hasn't done all levels yet but he played through most of them on Hard and tries to do the levels as good as 100%. The videos were entertaining so I decided to mention it in here.
In the Xbox version there are some differences compared to the PC version. The HUD being the most obvious one, but also the trees on the temple in Hatshepsut for example :)