We had this party for my son's 6th birthday and it's really not that difficult to do. His birthday is October 30th so we have fun doing off the wall type parties.   INVITATIONS We did the invitations ourselves.  I used Printshop and found some pictures of scientific type pictures to use on the invitation.  I used regular paper but did the quarter fold style.  It's much less expensive to do these yourself and let your child pass them out.  CAKE   We had a lady we knew do a cake of a man in a lab coat. He looked like a mad scientist. She added gummy worms coming out of his pocket.  She made the cake for around $15.   DECORATIONS It's really the best if you have a basement to set this up in. If you have the foresight to plan ahead, you can buy Halloween decorations (such as spider webs and fake limbs) after Halloween in anticipation of the next year.  You can save a whole lot of money this way by hitting the big markdowns. Decorating is pretty easy. You just set up tables, put black sheets or table cloths over the tables and add spider web all around.  I took clear plastic jars with lids, added water with some red food coloring, and then placed fake body parts in each ones. You can use cheap plastic or rubber body parts because they still look eerie in the red water. We had fake beakers and other laboratory looking type items on the tables. We hung black on the walls to make it more eerie.  You can buy this in rolls and the price varies according to the thickness. We probably paid around $30 for a roll.  Dry ice is a must!  You can find this by looking on the internet or in the phone book.  It's really not too expensive.  Depends how much you want.  It's great for making smoke come out of the beakers or test tubes.  Also, it creeps up the stairs. Wonderful  for the atmosphere of the party.  Fog machines can also be used.   GAMES AND ACTIVITIES  We did some of the old standards for games but they take on a whole new feel with atmosphere. Musical chairs was one of the games I remember doing.  You could also add some the the things they do at Halloween Carnivals. One that would be great is where you tell the person they are touching eyeballs when,in fact, it is peeled grapes or worms when it's cold spaghetti. You could give prizes" to the ones brave enough to do it.  Also you could ask the kids to dress as mad scientists for the party.   PARTY SNACKS Food is fun as well. You could make hot dogs look like cut off fingers. Oreos into eyeballs by putting white frosting on them adding a black jellybean in the middle and adding red lines of frosting to give the bloodshot appearance.  Halloween cookbooks are loaded with ideas.  FAVORS Goody bags are pretty easy to do as well.  You can usually buy the bags pretty cheap after Halloween or you can do like we did and use the brown bags that the kids drew on to save a little money. Also some of the novelty Halloween items work as well such as  fake fingers etc. You could also get the candy that looks like body parts or if it's not near Halloween gummy worms would be great.  Be careful about the age of the children since real young children may not enjoy this type of party. Even my son's party had a few kids who were too scared to go in the basement.  I knew we had done a good job at that point! "