I would just like to say Draco Malfoys intelligence is highly underrated. Or at-least not given enough credit for. Although he is an not good wizard, I hate to love the character he was written to be.
reasons why:
In book 6, when Draco was coming up with a plan to kill Dumbledore, he hid in the room of requirements. Every single day he made a new Polyjuice potion of totally different students around the school, for Crabbe and Goyle to pretend to be while guarding the room of Requirements for him. That was an ingenious plan if I do say so myself
Draco was one of the smartest students of the school. He was a prefect, afterall.
Lets not forget the fact that Draco Malfoy was so observant as a 10 year old kid, he never met Ron Weasley yet he knew just from simple observations such as tattered clothes and red hair... that Ron, in fact, was a Weasley.
Draco, even when Harry had the Half-Blood Prince potions book, had almost as good of potions as Harry did, in Slug-horns class, without help.
Can we also remember the fact, that he thought of a whole strategy to sneak the DeathEaters into Hogwarts, just from Flint complaining to him about George and Fred Weasley, putting him in a vanishing cabinet.
^^Even Dumbledore complemented Draco for this, god bless Albus' soul.
Most adult wizards cannot even conjure the Imperius curse, yet he was able to put Rosmerta, under the spell, and do his bidding for him
Professor Snape is very good in occlumens, yet Draco sheilded his thoughts from him. Even Harry potter struggled with occlumens.
He made buttons during the Goblet of Fire that insulted Harry, and nobody could disenchant them to say something elses
Draco Malfoy did get an "O", for Outstanding in the O.W.L., and was in the advanced potions class
I know he was only teasing harry, but when he said "Oh look, Potter. You got yourself a girlfriend." Ginny and Harry did end up together.