The blood barrier was significantly more powerful than most other magic shields, which isn't surprising given you literally have to sacrifice a great deal of your own blood to cast it... In addition to its fantastic defences, it also allows you to make physical attacks through it without risking your own health. Unfortunately, casting magical spells through it is still impossible, like most other shields.
Harry continues fending off the crazed people and corpses, slashing, stabbing, and hacking any that attempts to attack his blood barrier. Fortunately, their weak attacks aren't nearly enough to even damage it, let alone destroy it...
Harry doubted that even a .50 Calibre bullet could penetrate it, so what hope did these shambling people and corpses have?
The only negative the blood barrier spell has besides the obvious cost of casting, was the fact that it was incredibly difficult to convert any part of the shield into other blood-based spells. Harry currently wasn't proficient enough to split some blood off of the shield and form it into a blood spike or some other spell.
Fortunately, it wasn't needed in this situation. It takes around ten minutes to finally kill the last shambler. Harry lets the blood barrier fall into a large blood puddle on the floor while he tries to get his breath back... Despite all his training, he was still only 9 years old, so swinging a stone blade at adult-sized corpses was terribly tiring.
"Fine work there, master." Kali says from his shoulder in her bat form.
He shrugs, "I just hope all this work will be worth it."
Harry carefully steps over the corpses after giving them a prod with his stone blade, making sure he wouldn't be surprised by one again. Once the coast was clear, he and Kali approach the exit that seems veiled in darkness, he looks over it for a couple seconds before raising a brow at Kali, "Do you know what this is?"
Kali shrugs her bat wings in response, "Perhaps some forced darkness spell? The magic in there feels the same as out here..." she explains.
"Think I'll die if I step inside?" he asks.
She shakes her head, "The dark is only that, an absence of light... If there was an enemy we would have heard, smelt, or felt it. You haven't been attacked yet, which means whatever is inside hasn't noticed us yet."
"Alright... Let's go inside then." he mutters, gingerly pushing his hand into the darkness, and upon feeling nothing strange, walking inside. Strangely, the inside of the room wasn't completely dark, it was actually quite well lit, the door where the almost tangible darkness lingered was still covered by the blackness however.
"Master, look." Kali whispers and Harry's eyes are drawn towards the end of the room where a large, clay statue of a tribal woman stands, both of its arms are held out, one with a blade, and the other with a friendly outstretched hand... A thick film of dust covers her, except for one part across her eyes, where something seems to have been removed.
However, that's not what Kali was referring to... Under the statue was a man wearing strange robes on his knees feeling around the ground, all the while muttering "Where am I... I can't see... Why... P-Please!"
The man seems to be under some sort of spell as his lack of sight was obviously caused by the strange, ragged-looking blindfold covering his eyes. Presumably, this was taken from the statue due to the similar shape that had been covering the statue's face.
Harry looks at Kali questioningly, but she just shrugs in response, apparently not feeling anything interesting from the man. Shaking his head, he tries to speak to the man, "Excuse me?"
...
The man stops muttering and looks up in confusion, looking around the room until he stops and stares in Harry's direction. Though, once he 'looks' at Harry and Kali he reals back with a snarl, immediately breaking into screams, "EVIL! YOU'RE HERE FOR ME!? YOU ARE AREN'T YOU! S-STAY BACK OR I'LL... I'LL KLL YOU!" he roars, pulling some sort of stick out of his pocket and pointing it straight at them.
"Master MOVE!" Kali exclaims as she leaps from his shoulder to avoid whatever the man was about to do.
Harry, trusting Kali absolutely dives to the side just as the man shouts the words, "BOMBARDA!"
A magic bolt shoots from the wand and shoots through the darkness covered doorway, travelling through the other room and striking a wall, creating a large explosion.
The cave trembled slightly at the strength of the attack, but Harry is more surprised at finding another magic user than suddenly being attacked for no reason.
"Stay still and accept JUSTICE!" the crazy should-be-blind magic-user shouts while stutteringly getting to their feet.
"Master, end him!" Kali commands while flying around the room.
Harry nods while dodging a sickly yellow 'Aruspices Dividentem' spell, he thrust his hands up to create a temporary stone barrier while flicking a finger-tip from behind the wall. This releases a small stream of flame that quickly ignites the magic user's robes, causing them to start screaming and try to put the flames out... After a moment of struggling, he finally points his wand at himself while casting "Frigus repugnans".
Once this is cast the flames stop burning the man's flesh and clothes, but this matters not as Harry had already telekinetically thrown his transfigured stone swords at him.
The man doesn't even seem capable of seeing the lethal projectiles coming right at him, instead, trying and failing to cast a spell while he's punctured all over. "AAAAARRRGGGHH! EE-EEVIL-EVvill-" he sputters out before falling to the floor, dead.
Harry breathes a sigh of relief as Kali lands on his shoulder, observing the corpse with an appraising eye, "Seems like this world's magic hasn't changed all that much... Still supplementing their magical weakness with foci." Kali states.