In the roughly 45 hours I've spent working on runs, I've come to understand how a lot of the glitchier mechanics in Besiege work. However currently there's no real good place to start for new Siegerunners, and I doubt many people want to spend the time to learn how the engine works before they can even work on setting new records. So, I've compiled some of the more useful tips, tricks, and general quirks I've noticed in the game in the hopes that this can serve as a starting point for anyone interested in joining the Besiege speedrunning scene.

[section=Bomb Boosting and "Starters"] Bomb boosting is one of the most effective forms of getting speed in Besiege. To bomb boost, one needs to turn on "Intersecting Placement" and then stack bombs on the same point. When you hit play, the bombs will fly along the x build axis at insanely fast speeds. If you can explode the pile of bombs before they spread out too far, then you'll gain an immense amount of speed away from the explosion, turning almost every part of your vehicle into deadly shrapnel. Bomb boosting is by far the best method of completing a lot of the "Destroy ____" missions, as the shrapnel from your vehicle can reach speeds fast enough to phase through matter and hit objectives behind walls, terrain, or enemy soldiers.

However you need to ignite the bomb pile as soon as possible, or else the bombs will spread out too far to be useful. This is where "starters" come into play. A starter is anything that can activate a bomb on command, things like canons, shrapnel canons, flamethrowers, and crossbows. Just point them at your bomb pile and they'll do the trick. However one of the more frustrating mechanics in Besiege is randomized firing lag - which I'll get into later - which means there's definite tiers of starters.

A tier (1-3 frames of delay) - crossbow B tier (3-4 frames of delay) - flamethrower* C tier (5-10 frames of delay) - shrapnel canon / flaming bomb D tier (10+ frames of delay) - canon *flamethrowers seem to explode bombs, but remove all acceleration caused by them making them mostly worthless.

This means that 99% of the time you'll want to use a crossbow to start bomb piles if all you're trying to do is create a shrapnel explosion.

[section=HitReg, frame stacking, and collision lag]

Now, based off of the last section it'd be easy to assume that the fastest way to beat a level would be to stack a pile of 800 bombs and ignite them all at once, blowing an easy 0:01 hole in any currently standing record. Well the issue with that plan is twofold. Firstly, explosive HitReg. When you explode a bomb pile, there's a chance that no momentum will be applied to your structure, effectively creating a burning scaffold instead of a makeshift shotgun. That chance rises with every bomb you put on the structure, and by the time you're up to a hundred bombs there's around a 75% chance the explosions won't apply momentum.

And again, that'd be fine if it actually boosted your speed through the roof when it hit that 25%. But again, another engine issue stops you: frame stacking. As far as I can figure out, Besiege attempts to rectify any hitbox collisions as soon as the play button is hit. This means that when you start stacking hundreds of bombs on top of each other, the game will "pause" as soon as you hit start and enter a state where the game is lagging but the level timer is still ticking. And the delay is very significant; I'll often get 100-150 millisecond penalties in addition to the completion time if I'm unlucky enough to get frame stacking in a run and when most records are down to 80-100 milliseconds, that's a run ending penalty.

Even if there were a method of acceleration that didn't have the ability to stack frames or depend on HitReg, you'd run into a brick wall when it came to actually hitting your target in the "Destroy ____" missions. Besiege seems to run collision checks with differing priorities. Almost as soon as you hit play, every NPC or entity hitbox is accounted for and is able to be hit. However building and terrain hitboxes draw their collision later, meaning a super fast projectile can blitz through a structure and not damage it if it's going too fast. This seems counter-intuitive to speedrunning, but this means machines are more about finding a balance between hitting your target fast, and hitting actually colliding with them.

[section=Play button versus spacebar]

This was a trick I only recently discovered, but for a while most machines had their starters bound to the spacebar, meaning as soon as you hit spacebar the crossbow (typically) would launch and ignite the bombs. However in play testing I've found that there appears to be some guaranteed lag when you use the spacebar over the play button. And not an insubstantial amount either: I was getting upwards of 20 millisecond faster times clicking play with the starter bound to mouse one over using spacebar. Again I'm not sure why this occurs.

[section=Crossbow seperation]

Again another glitch I've found in testing, it appears that there's a small chance when you place a crossbow that the bolt will always be locked to the same firing point, even if you rotate the crossbow. It's not something I think can be used to your advantage, but if your machine is suddenly hitting lower times it may be worth making sure that this isn't happening.

[section=Finishing Notes]

I plan to update this guide as more and more mechanics are found/discovered, but for now this appears to be the generally important stuff out of the way. If there's any suggestions on how to improve this guide, or glitches/mechanics you think I should go over I'd love to hear them.