listen i am always down to gush at people tbqh. i am pretty sure everyone in this thread is tired of me but i do tend to come running screaming
DID SOMEBODY SAY BJDS?!?!?!?!?!?! at the slightest provocation
honestly i haven't heard many things that are good alternatives. the real beauty of mr super clear that you're going to want to bank on is the difference in texture between resin and the plastic of monster high dolls. (there are some bjds made with similar plastic - hujoo's abs plastic line - if you want to look up on how to do faceups on them, too. they're also a much more affordable option on how to get into the hobby; I have a little mouse from them that was bout 40 dollars. still expensive but better than 130 lol). the only other thing i've heard people use is a gloss medium - modpodge seems to be pretty good for that - but that's for just little details you want glossy, like lips and the waterline of eyes. it's also painted on, not sprayed on, and trust me when i say trying to paint on something to seal in the entire face is REALLY FRUSTRATING because it pulls the pigment all around and destroys your work. the msc is an investment but a can will last you a good long while and it's worth it.
what you'll probably want to do is 1. wipe off the factory paint, 2. rinse, 3. then do a layer of mr super clear. this will give the pastels you want to work on something to grip onto. mr super clear is good for both sealing and for giving a working surface on both resin and the plastic, though the plastic is much more slippery than resin, so you really do want the msc there.
every time you do something you like, then think about doing another layer of msc. think of it like layers in photoshop or the oekaki. if you really like the eyebrows, go 'okay, i like these. i'll seal them in', and that way if you do something on top that you don't like, you can wipe that away and not totally obliterate the eyebrows you just did that you really like.
besides soft pastels, the other thing you'll probably want to get for doing faceups is watercolor pencils. it'll be super tempting but
don't dare pick up a sharpie, the ink will soak in and both look really awful with feathering/blurring and then be something you absolutely can't get out again because it's soaked into the plastic/vinyl.
you'll see people using airbrushes, too, in videos, etc - but it's not something you need to run out and go get. you can totally do the same effect very patiently building up pigment with just a brush and some soft pastels. just shave off the pastel, or grind it on some sandpaper to make the pigment into a powder, then apply it with the brush.
this is all very basic stuff i know but it's pretty much all the advice i have, so better to give it and have anything possibly be useful to you than not

i've not watched much of her stuff myself but it's been highly recommended to me multiple times, i think on this very thread in fact, but take a look at
https://www.youtube.com/user/NicollesDreams if you haven't already. she does both bjds and a lot of monster high repaints so she'll have better advice than me lol!