I had a quick go at coming up with a moveset for Isaac that makes use of all the elements of the game's battle system - standard attacks, psynergy, Djinn, and even summons.
Jab: A simple sword attack, like Marth's jab.
Dash: Isaac jumps and attacks the opponent (like his standard attack in the games).
F-smash: Skull Splitter - Isaac slams his sword at the opponent with brutal force.
U-smash: Gaia - The ground splits open, and large rocks launch upwards.
D-smash: Rockfall - The ground splits open around Isaac, and rocks fall into the opening.
F-tilt: Punji - Isaac strikes at the enemy with a bamboo weapon.
U-tilt: Thorn - Quickly launches a small shoot of thorns upwards.
D-tilt: Quake - Causes a light, short earthquake just in front of Isaac.
(I got stuck on aerials. Isaac is a Venus adept, there's not much for him to do in the air, unless he borrows some Jupiter psynergy. I imagine they'd mostly be sword attacks similar to Marth's.)
Grab: Catch - Grabs the opponent and pulls them towards Isaac. The hand remains to hold the opponent until they break out.
Pummel: Isaac swings his sword at the opponent being held by the Catch hand.
Throws: The hand tosses the opponent in the chosen direction.
B: Flint (Venus) - Flint empowers Isaac's sword, allowing him to launch a strong attack. Hold B to charge.
Side-B: Sleet (Mercury) - Sleet appears and blasts ice at the opponent. If it strikes, has a small chance to reduce the victim's damage/launching power.
Up-B: Gust (Jupiter) - Isaac jumps up, and Gust strikes at the opponent with one or two blasts of Jupiter energy. (or should it shoot downwards, like Robin's?)
Down-B: Reflux (Mars) - Counters an attack.
His B moves are all Djinn. Like Djinn in the game, they boost Isaac's stats while they're set, and using them allows you to perform a powerful attack, at the cost of slightly weakening Isaac's normal attacks. When an attack has been used, press its button again to reset the Djinni (after a cooldown of about 20-30 seconds). The exception is Gust, which automatically resets if Isaac is struck while off-stage and in special fall (this is so his recovery doesn't reach Little Mac levels of gimpability).
If you unset all four Djinn, however, you become able to summon either Zagan (B) or Megaera (side B). Being such strong attacks, however, they have high start-up and ending lag, and you leave yourself open to being launched before the attack actually comes out (and since you have all your Djinn unset, you're going to go
far). If you successfully get the summon out, all four Djinn go into a cooldown of 30 seconds, after which they automatically reset, one-by-one (about a second or two between each).
Final Smash: Judgement
His favourite character was Felix, mine was Isaac. I guess it was one of my first RPGs and the silent nature of Isaac made him my favourite as I could imagine his personality, till GS2 anyways where I liked his spoken role as well.
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