Is retrying from checkpoints allowed in IL runs? I only ask because the rules don't specify. Personally, I think that it should be allowed, mainly because of Level 13. The reason is Thunderwing's patterns. If you have a good first phase and a bad second phase, you should be able to retry from the checkpoint at the beginning of the second phase, due to the fact that Thunderwing as a whole is random enough to the point where you pretty much have to retry multiple times to get a fast run. My best ever is a 4:06, but that isn't really something that's all too possible to achieve on a one try.

Admittedly I don’t run this game and am just the series mod so others with more context should feel free to chime in, but based on experience with other games that sounds completely normal for a speedrun. It sucks that there’s some random chance your run won’t work out, but it comes with the territory—the RNG is part of the game, and we’re speedrunning the game, so we have to deal with the RNG.

Many games are far worse at this, like getting an hour or more into a run before you learn whether the RNG is going to make you reset. It’s not unusual to spend hours, days, or even weeks perfecting a four-minute run (e.g. Refunct).

So I empathize, but I’d call this a hard no unless an overwhelming majority of runners agree.

(btw I assume you mean splicing a good run of each section together to make a segmented speedrun, not just restarting while the timer keeps ticking)

Actually, the In-Game Timer is interesting. If you get to a checkpoint with 3 minutes flat, and spend, say, another 2 minutes after the checkpoint and then retry, it resets back to what it was at the time that you got that checkpoint. So actually, it wouldn't be spliced, it would just be a lot of retries. However, in hindsight, if this can't be an official run, I could always just upload it as an unofficial run. (Of course, just as a video, not to Speedrun.com)

Oh, I didn’t realize people used game time. I can enable a setting on speedrun.com to ask submissions for both real time and game time, is that something that would make sense here?

I don't know if that would make sense or not. I'll upload my time and share the link with you and let you see what you think.