Place this clip after the promise is made on screen and before the reaction shot that pays it off. Pair it first with a cash register or gift reveal effect for a normal present, then follow it with a dragon roar for the fantasy escalation your scene needs onward.
About this sound
This clip is a Russian voice line insisting that dad promised Morty a dragon, delivered as a direct plea about an unkept promise. It feels pleading, funny and slightly exasperated, like a kid refusing to let an outrageous reward be forgotten, which makes the demand sound both sincere and absurd at once in everyday conversation.