Yea...so, this is pretty pointless.
Why not make it 3 Samus's with Team Attack turned off? or 3 projectile spammers with Team Attack off? The challenge has obviously been crafted so that it is beatable and also not very difficult, you simply need patience. Why do I say this? The problem with computer players is simply that you need to find a pattern or technique that works, then abuse it. So, in an effort to point out how pointless your challenge is, I did everything you said, with items On and with items off. I simply ran off the stage at the beginning with JigglyPuff, used the rising pound, got all the characters to the edge, then I came in, pounded them once, touched down on the side of the stage to reset my jumps, then proceeded to run away again off the stage. I repeated this over and over until I had taken away 5 of their stocks (per character, actually bowser lost 7 stocks cause he suicided a few extra times). You know whats funny? I took 7% damage the whole time, all from Bowsers flame.
The challege was no different with items on, so the item comments was pointless, all it did was let me have some fun cause I got bored so quickly abusing the same tactic over and over, so I landed, picked up a fan and started wailing on them, of course they ended up doing damage to me this way simply because I broke my strategy that would have lead to an easy win but simply required patience and repeating the same trick over and over, and since it worked for 5 stock I'm sure it would work for the other 94.
I like how you mention wavedashing, when it has no bearing on pretty much anything, its simply a common noob fallacy that you think wavedashing makes or breaks the game, when in reality it is simply an add on, chances are any regular tournament goer who is worth his salt can beat you without wavedashing, but the question is why should he? I'll leave this open for a few more hours then close it up.