Aight, here it is! I can't remember the exact measurements of the materials anymore, since my aunt and I just made it up as we went. But TBH, methinks this is a bit better, to make allowances for people's heights during creation. Who knows, maybe you can make a tiny one for a 5-year-old kid on Halloween =P
Black rubber strip made for gripping
Spray paint (silver and gold)
Chain (from a crafts store)
Some paper mache strips (optional)
A small-ish length of wire
So first off, we cut a PVC pipe about 2 1/2 feet (you can make it longer or shorter depending on your height, but this remains a good length for most people =3) with a saw. Then we used it as a 'base' of sorts to measure out the main parts of the 'key', like the bow-like handle and the blade. Remember to 'cut' the handle in half along the pipe. You can use templates from the internet for this part, or you can make your own template. But more or less, proportions are as follows: the 'bow' should be around one-third of the whole weapon, while the 'blade' of the 'key' should be one-third of the remaining space. Another thing to remember is that the ideal length of the handle allows for two hands to grip it without hitting the sides of the guard.
Also don't forget to make the Mickey-head~
Now that we have the handle and the blade sketched out, we cut two pairs from the handle-halves and the blade in illustration board, and then cut a third batch from the cardboard. Basically, we sandwich the cardboard between the illustration board slices, then tape the whole thing to the pipe. You can 'pad' the insides of the handle to make it taper away from the pipe if you want at this step, but it depends on your tastes. My aunt and I didn't pad it when we made ours, so yeah. Plug the ends of the pipe with leftover illustration board (The top 'plug' should have a tiny hole punched through it and a wire looped so your chain has something to hold on to), and add two strips of illustration board along the top and bottom parts of the handle where it meets the pipe. You can look at a picture of the key for reference if you want at this step to make sure it's accurate =3 Then we taped the whole thing down with near-liberal amounts of masking tape, both to hold the whole thing together and to 'mask' the loose ends and gaps.
Paper mache is optional at this point, but if you want a 'clean' look, and are a bit worried about the tape coming off, I suggest only a light layer covering of paper mache on the handle and the blade. You don't want this too heavy, of course.
So after the taping, or letting the paper mache dry, we then start with the painting. Put some tape just below the bow-handle in a single, thick-ish strip. It's fine if you accidentally paint the pipe part of the handle itself, since we're gonna put the rubber grip there later. So go nuts with the spray paint~! Of course, it's gold on the handle, and silver on the blade, unless you're making Mickey's Reverse Key. Don't forget to paint your Mickey-head keychain as well!
After it's dried, remove the tape below the handle, and attach the rubber grip with some rubber glue on the pipe part of the handle.
DON'T USE SUPER GLUE. SERIOUSLY. Rubber + super glue = BAD.
Now all that's left is punching a hole through the Mickey-head keychain, and attaching the chain to it and the top of your newly-minted Keyblade!
Of course, this Keyblade's sturdy enough to take more than a few hits, but take care to make sure the handle and blade don't get too detached!
(ours is a few years old at this point and we just patch it up a bit every now and then. but tbh we don't fight with it much >X D)