Alright, it's time to make a horibble moveset that nobody would take seriously!
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Cloned from: Link seems to be the best IMO. I want to play off the idea of psyenergy being invisible for the most part, so any attack using it will consist of having gust around him of some sorts. PRACTICAL THINKING.
Stance: Isaac would be holding his sword with one hands and in a relaxed way, similar to Marth. His other hand will be used primarily for psyenergy shenanigans. While far from the games, it makes his movements far less awkward to map out.
Running: Isaac's overworld running from the games. Cuz it's adorbz.
Standing A: Isaac does two quick kicks side to side and then Isaac uses psyenergy to push the opponent. Remember, most psyenergy is invisible.
F-Tilt: Isaac does something similar to Luca's F-Tilt, but made to appear like something closer to psyenergy. ...Is that practical? I dunno.
U-tilt: Isaac does an upwards pierce in the direction he's facing. Starting from his torso, it'd be approximately a 60 degree angle upwards
D-Titlt: Isaac does a downwards pierce in the direction he's facing. Same thing as above but downwards.
Dash Attack: Isaac uses N64 Link's jab.
F-Air: Isaac uses his standard attack animation from Golden Sun. It'd be a quick slash that covers his shoulder to his thigh IIRC.
B-Air: Isaac does a stand behind him coming right from his torso.
D-Air: Isaac uses ground psyenergy to push himself slightly up and his enemies down. I believe this should consist of Isaac using his non sword hand and having it opened up. As the move has a hitbox, some glowlike aesthetics should cover his body to show he's using psyenergy.
U-Air: Isaac does Link's classic up tilt.
N-Air: Isaac could have either a sex kick or Marth's N-Air, either way works.
B: Isaac does his assist trophy motion, albeit heavily altered. The hand grows larger the longer you charge. Simple.
Side B: Isaac releases a Djinn, which charges at the enemy, then retreats back into Isaac. Preferably Venus.
Down B: Isaac forces the earth around him to shake, animation is similar to Wario/Charizard's down-smash. Can lead to tripping and allow followups. It would be chargable and the longer the charge, the larger the range. The hitbox would end around half of a platform of battlefield on either side of Isaac. It'd naturally have to be a quick charge.
Up B: As silly as it sounds, It'd be fun if Isaac had a Tiger-blade (Tales of Symphonia) like motion for his Up B. I just think it'd be fitting for some reason.
F-Smash: Isaac's charge his sword like Tink's. It'd be nice if the sword had kinda a glow affect while this happened, complete with the "____ is making a howl!" sound effect
D-Smash: Isaac forces a small earthquake. Similar to Charizard's downsmash, but far faster and far smaller in terms of hitbox.
Up-Smash: Isaac uses Tink's slash from classic Brawl, just bcuz.
Final Smash: Got nothing
. Perhaps Isaac jumps into the air and meteors down and it has a huge hitbox.
Taunt 1: Isaac points his blade in front of him
Taunt 2: Isaac tries to put away his sword, the curse sounds effect happens upon trying and Isaac takes it out of his sheath again.
Taunt 3: Some sort of jab at him being a silent protag. Golden Sun tradition. No idea what specifically however.
Alt: Old Isaac. Obvious choice
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Whew... not too bad...