I don't know what you schmucks are using in 2021 to play this modded Minecraft, but I have been hooked on MultiMC for years now. I think it is a brilliant launcher, and it feels very familiar to someone that is used to installing mods the old way (without a launcher). Thankfully, MultiMC automates the whole zipping process, so you never have to open a jar file.
So, if you can't figure out the normal Minecraft launcher or whatever, here is a brief overview of how to install Better Than Wolves using MultiMC.
The interface is pretty straight forward. You can right click to make a new instance of the game. Select version 1.5.2!
Then, you can click "Edit Instance" in the right sidebar to add some mods.
Keep your eyes on the right sidebar. Clicking "Add to Minecraft.jar" will allow you to select a zipped mod to install automatically.
The mod in question just need to be a zip file containing all the mod files. If you are installing CE, you don't need to do anything. Just download the client file and select it with MultiMC! If you want to play any Flowerchild versions, you probably need to take out the client files and put them in their own zip.
NOW, if even that is too hard for you (and trust me, I get it), you can also just import instances from other people with the click of a button. Someone with a fully installed Better Than Wolves can send you the file. Discord is quite handy for stuff like that.
The only trouble I can foresee with MultiMC is that sometimes it doesn't detect your java version quite right.
