In my game vs Hogar (duel07) on map Hexagon, in turn 5 I met 2 mummies UL 10 in tier1 ruin. My Valkiria had 10 UL, killed one which is harder than clearing any possible tier1 ruin, then died. After that I could see any ruin guards on the map and more impossible guards existed: for example 4 mummies in tier2 and 5 vampires in tier3.
Checked map in editor - ruins had random guards (I see its not even possible to pre set 2 mummies in tier1 ruin).