"For being so old, you aren't very good at checkers." you say.

Ask him if he knows any other games we could play!

"There was a game where people would hide and I would find them."

Ask Matthias to explain the rules in further detail. Just in case it's some kind of "I find you, and then I try to kill you" sort of affair. You never know.

"There were no rules. I would try to kill people and they would try to postpone their fate by hiding."

"Come on, no. Here are the rules. You cover your eyes and count down from 60 while John and I hide. When you get to 0 you say, 'Ready or not, here I come.' and start looking for us. The last person you find has to look next. No killing what so ever."

"I understand." he says as he covers his eyes . "60, 59, 58..."

We could just hide face-down in the blood sea (already dead so no risk of drowning) and cloak ourselves with our toga (which is, of course, also made of blood).

You still need to breathe.

"48, 47, 46..."

Create a bunch of kobold shaped blood decoys and get the fuck out of there. Hide in the first convenient spot you find after 40 seconds. Watch to see what Matthias does to the decoys. Confirm that he isn't just going to strike you down when he finds you.
Modification: Just make one, and hide it somewhere super obvious, like just under the table.

"3, 2, 1. Ready or not, here I come!" He uncovers his eyes and looks around. "I have found one..."

"Grawr?" he asks.

Once you are satisfied that he is not going to smite you, you release the decoy.

Try to see through John's eyes. Use him as a spy on Matthias's movements.

You are now controlling John.

Mathias is standing, looking around the bloodscape.

A flash of light at the corner of your eye breaks your concentration.

There is some sort of small blinking light at the end of this tunnel.

Check it out first. Then come back and talk to Matthias if it proves to be an es-capay route or some such. What if it's like, a divine macguffin of bloodromancy power? We should definitely have that ourselves.

Also if it IS an escape I think we should officially resolve to take Matthias with us and trust in the power of friendship. I am fully aware of the potential ramifications and say we..... *snrrk*... ROLL with it.

You get closer and let your eyes adjust.

In the middle of the chamber floats a massive three-sided pyramid made of dark smooth stone.

Shiny...

You want to touch the shiny.

You touch the shiny.