Look at it for a while and it will open. You will see a mist first then you have 30 seconds to use Raiden's Staff

There is another Arkedia??? (outside the Shadow Spiders Cave) Called the Secret Room same thing look for the mist.

There is a rumored third one in Frosts path but I haven't seen it

The bloody wall and the Shao Kahn statue both have the same criteria - you need Raiden's staff.

Back up from the tile and wait. The floor in front of the wall/statue will light up when its ready to accept Raiden's staff. You won't have to wait more than one minute - I forget exactly when on the Krypt clock that the tiles light up, but you don't have to wait long.

Nothing special - just leads to two extra rooms with overpriced brutalities.