Quoted from GorillaBiscuits:
the sarcophagus lock is only meant to hold one ball right? Even during sarcophagus multiball? Think I’m at 100% here and just want to make sure lol.
Here's a good summary from Fytr as to how it should work:
"So at game start you hit the sarcophagus captive ball twice to open the tomb. Sarcophagus raises up to accept a ball.
Shoot left ramp to load the ball into the sarcophagus lock. Sarcophagus lowers to flat again, with locked ball immediately behind the captive ball.
Hitting captive ball now will cause the locked ball to roll back to the end of the sarcophagus trough and hit the switch, which registers your hit of the sarcophagus (grants a mummy letter).
If you open the tomb door again the sarcophagus stays flat as it can only hold one ball. The next ball will roll off the top of it and down to the upper left flipper.
During Mummy multiball (i think) the sarcophagus will lower to dump the locked ball into the underworld scoop which shoots it out.
Also during another multiball (Trooper?) the sarcophagus will raise up a bit and if you hit it the locked ball will be knocked out and into play (add a ball). "