Tunnel Skip

Tunnel Skip is OoB glitch made by AKheon ⁽¹⁾ to skip most of Mission 5 fights using V's Skewer wall breach tactic. Later on the skip got optimized by the community to avoid all tunnel fights, which made Elder Geryon is the only mandatory fight that is the end of Mission 5.

Origin

AKheon shared the Skewer wall breach tactic within community.
KaioSekka ⁽²⁾ made semi-reliable setup for getting out near the start of the level.
Landing down on the underground tunnel has multiplie variations made by each runners.
^03/04/2024 new variation made with Red Orb cache being the main visual cue instead of the barrel Lock-on.

Trick Requirements

To perform this trick correctly, you need the following:

PC runners should run the game at 120 FPS to make wall breaching more reliable.
Skewer

Trick Mechanics

Tunnel Skip exploits Skewer to reach OoB by clipping through the wall:

Step 1: Get V on the corner and move Shadow near the root. On this spot V is at the right height to get clipped through walls by Skewer; all you need to worry about is the angle of the spike while V is moving forward. With careful use of lock-on, you can keep adjusting the angle a little by little until you finally find the one that pops V through the walls.
Step 2: Once you're on the other side, running to the left and dropping down lets you reach the underground tunnel fight early. However: the location matters a lot as there are plenty of variations that you can use. Refer to the Video Demostration and pick the one that suits your consistency.

Other Notes

For console runners, it's advised to spam Taunt all the time so that V becomes suspended in air doing an Air Taunt once he finally clips through.
NG+ has back up variation of the trick where V jump down through a hole in the floor before the small pipe. This drops him down on top of the underground tunnel fight arena as the fight is about to start. Summoning Nightmare and using Promotion allows V to get in-bounds. NG has to restart checkpoint if V ever gets stuck from a bad Gambit timing.
The timing is critical here. If you fall too close to the level and hit one of those invisible loading zones, the game will softlock.
The camera adjustment before underground tunnel jump is primarily done to get a good visual cue on when to throw Gambit and each player has their own adapted method.
Underground Tunnel - Barrel Lock requires to jump directly out from the gap in specific pallettes as demonstrated in the video before timing Gambit
Underground Tunnel - Orb cache visual cue requires to use old variation jump but to Gambit right after the Red cache disappears by split seconds. It will land on the area regardless if the map instantly loads or not.

Video Demonstration

Clip setup case 1. Sometimes V falls from this which will cause him to respawn either in-bound or out-bound so he could jump on the other side.

Clip setup case 2. This usually pervents enemy spawn that pervents you to get extra door cutscene and allows V to sprint with Shadow for free at the end.