­Tomb Entrapment gives me another in the continuing series of almost-pointless but secretly-squiggly cards.

The way you put this as an instant reminds me of the old horrible phrase "already on its way to the graveyard", like on Gate to Phyrexia and Ashnod's Altar...

you could introduce a new card type that can be played only during the resolution of a spell or ability. call it Interject.