Common "mistakes" with Easy backups (your run is not dead if these happen):

Breaking Leg Eye in 2 Hits (or the rare 1 hit):

I see people reset for this sometimes and you really shouldn't. There’s a few options, two of which either switch to the next knife after breaking the shoulder eye (safer, but riskier for durability) or after breaking the back eye, which is likely mandatory for 1 slash and also eliminates more durability worries for Tyrant, which does have a minimum (it will depend on your ability on Tyrant, but i’d say below 250 can get risky for me, unless you practice Tyrant a lot).

Durability worries are a bigger deal if on a run with bad DA, which would be a damageless run (1200 hp), a run with just a lick or dog hit (1020 hp), or just a dog hit with door cancelling stagger (1100 hp), so you really don’t want a 2 slash on a bad DA run honestly. Good DA run for reference is either normal grab setup (860 hp) or grounded licker slash (900 hp) (all these videos are recorded with optimal DA as if you were at 860 btw and these are possible at higher anyway. Durability after boss is what's most affected anyway).

Shoulder Eye Swap Video: Back Eye Swap Video:

You can also do the bossfight like how Furetto does to avoid this 2/1 slash situation entirely,  but I would not really consider this a backup and more or less a different G3 strat. It involves knifing more on the shoulder eye to break in 4 and then switching the knife after shoulder eye breaks. I feel like it can be risky to adapt to this strat if you can’t already break G3’s shoulder eye in 2 slashes most of the time with the other method because you will be at a deficit compared to normal for you. This strat does not seem any faster or slower than the regular as far as its currently known, so it’s a viable option.

Furetto Method for G3:

Missing Back Eye:

Anyone who has tried the knife only strat knows how hard it is to break the backeye. If you whiff all 3 knife slashes, prepare to make your way towards g3's front, then shoot his back eye. If it was a close miss, it can break in 1 shot, but often in 2. It isn't a hard shot to hit once you understand where you are aiming. Getting a crit on this eye can kill the run and be careful to knife low after eye breaks to not accidentally hit his front/make him get up instantly. This backup's only downside is losing about 2 seconds, but it’s better than a dead run to be honest.

Missing Back Eye w/ Knife Backup Video:

Breaking Leg Eye in 6 Slashes (tricky backup):

On the polar opposite of the spectrum for G3, breaking the leg eye in too many slashes is also problematic (and I'd say in 7 is likely a dead run). What you want to do is only go for 2 slashes after breaking leg eye and go towards the wall on the left, then do the fight as normal.

Here is a video with timestamp of backup, which was actually a former world record only possible because I knew of this backup (sorry for video quality):

Leg Eye in 6 Backup Video:

In the clip, I got a fast slam at the cost of a fast shoulder eye knife due to space. You can walk farther back for a slightly slower/farther slam that allows for more room to knife shoulder.

That’s all I can think of for now. If there’s any other situations you have questions for, hit me up on Discord, Twitch, Speedrun.com or whatever and I’ll happily answer.