How can I make a sound like a snare drum hit using my electric guitar and multi-fx pedal? I imagine it's possible to get a more "authentic-sounding" snare hit than just strumming muted strings without any effects, but I haven't managed through my own experimentation.
The first thing I would do is put lots of nonlinear distortion on the signal, to squelch the actual guitar-string character. With sufficient distortion, any sound like muted-string-strum will become more or less a white noise burst, which is also the most important component of the sound of both a snare and hi-hats.
Unfortunately, almost all guitar distortion effects work by the principle of clipping, i.e. they boost the signal beyond what the circuit can actually handle, so that the peaks are truncated. The transient edges of this truncation are what causes the bright fuzz sensation, but as a side effect, the signal is strongly compressed because the small-level is boosted while the louder notes are simply reduced to a square wave. That compression is normally desirable for guitar, but if you want percussion it works against you. There is also a completely different kind of distortion which instead clips the low-level signal to zero. The recent Gamechanger Plasma Pedal is based completely on this. Software-based distortion such as iZotope Trash can also do it easily.
After such a distortion, the signal will sound very percussive and noisy, but it won't have the spectral character of the perc instrument you actually want. There's a nifty way to get that though: convolution between white noise and a given sound sample will give you the spectral details of that sample its ring-out sound, while retaining all the dynamic response of the noise “trigger” signal. Convolution is nowadays a standard part of every amp simulation. It is usually used to simulate the speaker cabinet and room reverb, but you can also load any other sound into it, such as an actual snare drum sample. In fact, iZotope Trash used to come with a snare “cabinet” sim, which does just that. Most amp sims until recently didn't allow loading custom impulse response files, but I think the newer ones like Bias FX do. In a DAW, you can also use a convolution reverb plugin, which does exactly the same.
The result of all this will sound neither like a snare nor like a guitar, but it will be usable in broadly the same musical way.
Related: I imitated an acoustic drumset using only a simple Monotron synth and the convolution technique, i.e. basically guitar effects, when I made this – ahem... very mature video ages ago:
I also made another video then explaining the setup used: