Okay, I've heard some people have problems reading masterposts, so im going to quickly (as much as possible!) summarize the totempulse au here to help people understand better. If you have questions about any specific part, feel free to send an ask or ask in a reblog!
The basic premise is that using lots of totems has gradual permanent effects on the user. Specifically, death resistance (better regeneration, taking less damage, slower aging- all that good stuff). These effects are called totemification (Tango named it). However, they don't work on void damage, because totems don't either.
It also has side effects, which are becoming more totem-like. Side effects include golden skin, emerald green eyes, wings, and producing totem particles. One of the more extreme side effects is shrinking. It takes a lot of totems to get even a few inches shorter, but quickly speeds up until they become the same size as a totem.
The plot so far is that Impulse developed totemification. This was discovered during a boomers job, in a situation where both Impulse and Tango should have died, but only Tango did.
They then told Zedaph about this strange occurence, and together team ZIT experimented and discovered both the effects and cause of totemification. Impulse also flew into a wall a few hundred times (with totems) to advance the effects. Xisuma saw this, and later questioned Impulse about it, leading to him knowing about totemification as well.
Then Tango decided to find out how totemification works by looking in the code. Then he found out he could increase it. Then team ZIT did more experiments, which included getting Impulse and Zedaph totemificated enough that they got wings, and trying to find out what maximum totemification did. That last one was tested on Impulse, and the effects were that he became tiny (and gold, and winged, and sparkly, but he was already).
Impulse doesnt enjoy being tiny. Its kind of hard to do redstone at this size. Unfortunately, this is when Tango discovered that he couldnt actually decrease totemification.
Zedaph eventually discovered that exposure to the void can reverse totemification effects. How he found out? Falling into the void.
Now Impulse has to go into the void in order to get back to normal size. He is scared. He is especially scared because the void is the only thing that can kill him at this point. And Impulse does not want to die.