Ah, sorry didn't catch the from gheist part, but nightmare has an advantage against gheist, since nightmare's SOAs will work, but gheist needs to depend on leviaton to stop nightmare's really big abilities like kolos and kenny.
SOA = stop opponents ability
SOB = stop opponents bonus
It doesnt matter if you played your cards first. When your cards has SOB (like nightmare) then it will automatically stop your opponent's bonus, unless the oppont have SOB as well. Therefore, if you put SOB (nightmare) against SOA (as a bonus like Gheist) then Gheist's bonus wont be activated coz it is cancelled out by the SOB.