Transparency support for entities

Issue description

Yes, my almost-invisible mob is completely opaque, which ruins the surprise...

Issue comments

The current rendering system does not support this in any normal way as far as I know.

I believe Ghasts would be transparent if there would be any standard way to do this :D

there is this ghost thing on Mo Creatures mod, that is translucent (ghost style), so there must be a way for sure.

I know this is late.

So I actually just found out tonight you can get a transparent mob if you upload an entirely blank base texture for your entity, and then upload the true entity texture under "Glow Texture of Entity". The rendering is a little funky when certain things are the background but its essentially a glowing, transparent entity. For a jellyfish it'd probably be alright.

Otherwise you might wanna try your handing at custom coding.

if you wanna make a transparent texture for a mob in block bench, erase the area and set the opacity of your brush to like 100 or lower then boom