Used for Elis' entrance animation. Including an unused unblitting +
blitting function – apparently, ZUN wrote that one before the sloppy
EGC-accelerated wavy unblitting function that I decompiled way back in
6d2fa9f.
Oh well, the latter one is fine in context, since there are no other
sprites on screen during the animation.
Part of P0108, funded by Yanga.