Rewards for not taking damage from a boss?

I'd love that. Even just medals for bragging rights.

I'm all for the medal thing, not as much the exclusive usable item for the main game. Just because it kind of goes against the design philosophy IGA is shooting for, that -any- player can play long enough to get everything. If you can re-fight these bosses later in the main game, it could work, but otherwise you'll have a sore group of people knowing they're dealing with missables. You also have that as an issue to itself - does the game tell you these things exist? Say a skilled and leveled player that maybe only took one hit could have easily gotten it with a retry, but didn't know. Now he'll have to restart his file or play NG+ a new cycle to get it. This would probably happen to me - I don't like missables, but I also always play blind.

Such as I love OoE, but I'm not sure I even remember the medal thing. It sounds familiar, but it may have just struck me as coincidental lol. My memory isn't great either, though. What were we talking about? mmm

purifyweirdshard : you got medals for beating the boss without getting it, it was purely for bragging rights and if memory serves me right was not tied to unlocking any actual item or glyph, but to show yourself (and others too) that you were hardcore enough lol

I probably would give it its own section instead of needing it for 100% item completion. also, have it attainable from boss rush if possible.

Boss rush! That would actually be even better, since you set getting them aside for skill alone instead of overleveling!

I just went through the order of Ecclesia Boss videos and they do last on average 10 seconds with three of them having skippable text(Albus Barlow Dracula) and one boss where you can just walk into the boss door and start fighting her (rusalka) as soon as you enter.

Also the last two boss cutscenes we've seen in bloodstained are even longer. I don't think it would be hard to implement making them skippable.

I'm hoping that they add in the boss medal from OoE but change it up such that they're not required towards 100% item completion end-of-game rating.

If I would defeat some mid-game sub-boss without getting hit and get a boss medal, I'd say to myself "Heh, that's cool!" then just move on through the current game scenario and continue collecting shards.

Only medals. If you want perfect run for a less superb player, they need to run the boss over and over again. Instead, leave that feature to another mode, and lock those "cool items" in that mode.

Many of you probably heard what i'm going to say, because it isn't the first time i'm saying this, but for those who don't, here goes. In a event for game developers after Konami, before Bloodstained, IGA said that his technique to create bosses is to make sure a tester can beat the boss, with the equipment and level that are average for that moment of the game (expecting the player to be around the same level with the same gear) and see if the tester can beat the boss without taking damage after some tries. If he/she manages to do that, it means the boss is balanced enough.

That means that, ALL Igavania games has bosses that can be beaten without taking damage, and that, for sure, will be the same for Bloodstained. The medal thing in Order of Ecclesia didn't had any purpose besides bragging rights, as some already said. The game also didn't explained how you got them, BUT, since the game HAS a boss that can ONLY be beaten by not taking damage since all it's attacks are one-hit kill and if i'm not mistaken, you cannot be damaged by touching him (Wallman) everyone would get his medal and that was a hint that medals existed. But Wallman is one of the game's last bosses, so, i'm sure completionists could be enraged by figuring that out so late in the game.

I agree that could be achievments for each boss. No medal, no item, nothing like that.

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SIDE NOTE: Someone mentioned Rusalka. I really like that boss. Rusalka can walk on water like it was solid ground. Soma, in Aria of Sorrow, can have that skill by obtaining Undine soul, that doesn't come from a demon and is trapped inside a Soul Holder (a stick containing a soul of a demon that didn't showed up in the game). 
None of what i will say now is canon, but in my creative mind, i will always believe that Rusalka is actually the demon that owns Undine soul and her real anme is Undine, and that in Aria of Sorrow, some demons simply didn't materialize inside the castle and their souls were trapped in soul holders.

interesting Galamoth, didin't knew that.