If you’re looking to get the characters as soon as possible then you will want to simply play through the levels as quickly as possible, not bothering with True Wizard, Red Bricks or unlockable characters. Then devote a replay to getting every single last thing you can in a level all in one fell swoop. A few of the characters can easily be nabbed while playing the game like normal; those will be noted in the list.
1.1 – The Magic Begins
Mr. Ollivander – Inside of the bank, once you open the first gate with Griphook look to the left. There is a chest here that you must use a Reducto spell to open.
Tom the Innkeeper – From there head the opposite direction to find another Reducto locked chest.
Griphook – Upon arrival at the storage vaults there is a chest directly to your right with another Reducto lock. Blow it open to get the valuable Griphook and his key.
1.2 – Out of the Dungeon
Ron (Girl Disguise) – On a free play of the level use Hermoine’s book to open the bureau to the left of the starting point.
Harry (Hogwarts) – Down the hallway from the bathroom is a silver lock on a writing desk. Blast it open to reach Harry.
Madam Malkin – Once you spawn into the bathroom go straight to the left to find a silver lock on a locker. Blow the lock then open it up to find Madam Malkin.
1.3 – A Jinxed Broom
Fred (Quidditch) – When you reach the tunnel that Ron has to send Scabbers through use Reducto on the chest to the left to get this token.
Harry (Girl Disguise) – After getting to the top of the previous area you will reach another LEGO puzzle. Take out Scabbers (or Hermoine’s cat) and send it under the wooden stairs to reach Harry.
Marcus Flint – Past the previous token you will enter an interior area. Here use your Dark Magic to blow open a cabinet and reveal Marcus.
1.4 – The Restricted Section
Harry (Pajamas) – Blast open the metal container near the bookcase on the right side of the room.
Filch – When you enter the second area of the library go straight to the far side of the room and use Griphook to open the safe to reveal Filch.
Neville (pajamas) – In the final area of this level there is a Dark Magic cabinet in the far corner of the room. Pop it open to get the token.
1.5 – The Forbidden Forest
Fang – To unlock Fang you need to use Fang or Hermoine’s cat to dig in the first area of the level. It is located in a hidden, off-screen area in the southeast part of the level you start on.
Hagrid – In the third area you will see a sealed chest, blast it open with Reducto to unlock Hagrid.
Draco (Hogwarts) – Found just past where you got Hagrid. Go to the upper level via the LEGO bricks and use your Dark magic to pop open the rock and get this token.
1.6 – Face of the Enemy
Harry (Slytherin Disguise) – In the room with all of the flying keys a treasure chest with a Reducto lock can be found in the far corner. Blow it open to find this token.
Professor Quirrel – When you enter the chessboard room use Dark Magic to destroy the fallen chess piece right by the entrance door.
Ron (Cardigan) – On the far side of the chessboard room is another fallen black piece, use Dark Magic to break this and get the final token of Year One.