The effect of "Faustian Bargain" targets the Special Summoned monster on the field that is to be sent to the Graveyard. You can also target a monster on your opponent's field that was Special Summoned.
"Faustian Bargain" cannot be activated if you do not have any Level 4 or lower Normal Monsters in your hand.
If you do not have any Level 4 or lower Normal Monsters in your hand when resolving "Faustian Bargain", then the Special Summoned monster is still sent to the Graveyard, even though you cannot Special Summon a monster. At this time, the opponent may check your hand to verify that you do not have any monsters that you can Special Summon.