I've already spent several solid hours trying to beat this boss, reading guides and watching videos to no avail. I think another hinderance to my progress is the fear that I will come across another boss that is similar or even more difficult to pass. If this happens, I think it is likely I will lose all interest in continuing on with the series.
It's a shame because I really enjoyed the higher paced, simpler gameplay of this JRPG (I generally prefer more complex mechanics, but the bump system is pretty new and fresh to me). I never felt like I was grinding for gear and levels and money which is a nice change.
I am maximum level with all silver gear. The rings as I discovered don't do anything, which is a shame.
When the battle starts I try to keep close to the bats as I've learned that they all fly in a line directly towards Adol, then I pretty much trace around the outside trying to keep the bats as clustered as possible, trying to create a bit more distance so that they will take on the solid form.
Attacking is made more difficult because of the very tiny window that you have to do damage when in that solid form (vaugllion is the name from what I've seen online). It also seems that I can miss if I attack too early as well (this causes some strange attacks where I will somehow land an attack part way through him and end up on the other side).
My best result so far is having the boss a little below 1/2 health before I am killed. Recently I've been modifying my speed and tracing a rupee run pattern rather than going corner to corner, which seems to have improved my odds a bit, but it is still very rare that I can get him down to half health.
Any other tricks that you Ys I veterans use to pass this boss? will there be bosses in the future that have this same level of frustration?