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Do you have ANY idea what a mindgame is? A mindgame is something you do to mess with someone's head. When I'm taunting someone, I'm playing mindgames with them. When I'm showing off my mad skills at the other side of the stage and the other person goes "oh crap, this guy's good!", that's a mindgame. When I drill massive damage on someone and send them to the moon, that'll work as a mindgame too. When I act like I don't know what I'm doing, then suddenly destroy someone, that's a mindgame too.
If you're talking about advanced techniques, I'm afraid you're sadly mistaken. Several of the things people call 'advanced techs' are actually in the manual. Some people just never bothered to read it. I LOL'd when I saw an "all-new advanced tech" people just figured out not halfway through the booklet.
As far as the "it's not in the rulebook so it shouldn't be in the game" argument goes, that's crap as well. OMG, the secret characters aren't in the rulebook! They have to be taken out of the game!! Oh no, the rulebook doesn't say anything about secret stages, they're cheap and need to go! The rulebook doesn't mention short-hopping, so it must not exist! Fast-falling needs to go, too! Oh wait, L-cancelling isn't mentioned in the rulebook, even though the script for it is clearly in the game! It must be removed too! Wait, it doesn't say Zelda's up-B does damage, so it's cheap and has to be taken out! The booklet doesn't mention DK being able to carry characters around, so that has to go too! Liek OMG, more than 20 items aren't in the rulebook, they must be ELIMINATED!!!
For your information, wavedashing is nowhere near overpowered. The only reason people lose when someone uses it is because they think it is and start overreacting. It's actually pretty simple to beat, and is completely outperformed by crouch-cancelling, L-cancelling, and dash-dancing, all of which are legitimate character techniques and are written into the very coding script of the game itself. On another note, WDing is also in the game's script. i.e., it's not a glitch and is actually supported by the people who created it (also known as the 'game designers').