I have a polybag of LEGO pieces and need the set they go with.
There is one 6x6 large black square and ten light gray 1x2x2 with a small bag inside.
What set are they a part of?
This is 41611: Marty McFly & Doc Brown, based on Black Plate 6 x 6, two of Yellow Brick, Round 2 x 2 with Axle Hole, at least 8 Red Brick, Modified 1 x 1 with Headlight and the Black Brick, Modified 1 x 2 x 2/3 with Studs on Sides.
For future reference, you too can use Bricklink to identify the sets by entering the known parts into this form, to get an answer like this.