The art is super adorable. *^.^* Welcome back Hyro!
Unlike Zblader though, I think that the cost should remain the same; even in the upped format, you're technically using 4
(Upped Pyramid + Upped Sundial) to summon an upgraded Mummy, which costs 3
. If you don't draw any Sundials (or worse), your Pyramid gets pwnzoned by an early Deflagration or Steal (I'm assuming Pyramid doesn't apply to itself), then you don't generate that Mummy, and the effect fails. This is assuming only one Pyramid is on the field.
...of course, does this stack? (as in, if you have multiple Pyramids in play, would they all generate a Mummy if a Sundial expired?) O.o