Very nice game!
As a point and click game maker myself, I know a good one when I see one, and this is amazing. Its ruthlessly hard, but its cool.
I'm stuck at the moment, so I am gonna wait for some tips or anything that can give me a clue how to kill the spider, but here is how to complete the costume for people who are still confused:
Get the comic and the stained pants from your bedroom.
Get the superglue, cutlery, cereal and the bucket from the kitchen. Use the superglue with the cutlery (from the kitchen drawer) to make the claws. Read the note on the table, it is talking about the lights for each room, make them match its description as you go along.
Go to the bathroom and fill the bath with water. Add the cereal to it to make it blue. Then use your pants on it to make green pants.
Click on the moushole by the bathroom door a couple of times to find the parents bedroom key. In there, turn on the stereo (that controls the lights in there), then go to the living room. IF all the lights are set right, the trapdoor should open. Down there grab all the stuff including the mousetrap and drill (there is also a crowbar down there and some bug spray). Use the drill on the bucket for the helmet. Use the mousetrap next to the boots in the living room to get them. Then your costume should be complete.
I'm stuck for what to do now, I'm outside, got all the items I think I can get, but nothing is working, tried combining everything in my inventory and nothing works so far :((