General Idea:
Undertale is a game where you get stronger when you fight, but the ultimate goal is to spare everyone and be kind. Thus, the moveset will revolve around getting stronger by doing damage, but being able to spare enemies to get rid of bad karma
Gimmick:
Frisk has a LOVE meter (level of violence) above their percentage.
Whenever frisk deals damage it will fill up the meter proportionally to the damage dealt, and taking a stock will fill the meter by as much as doing 50%.
Taking damage has no effect on the meter, but losing a stock resets the meter to 0%/
The more full the meter is, the more damage/knockback some moves will have. However, the higher your LOVE is, the lower your mobility, and it becomes harder to dodge attacks. However, you can use certain moves to get rid of LOVE and do powerful sparing moves.
What LV do you start at the beginning of the match? If I had to guess, it would be at LV 50 since it's the middle ground between Pacifist and Genocide. However the problem with LV 50 is that Frisk hasn't committed any violence yet and if you're at LV 0, there is no way to gain LV as Frisk in your words is a Pacifist at that point and there is no way for their attacks to gain any LV.
LV being gained from dealing damage makes it too easy to gain LV and from what I've seen, your moveset options are limited to pretty much using Neutral and Down Special if you're trying to become a pacifist and dealing damage will remove all the work you put into removing the LV.
Stats:
Movement-
By default, ground and air speed would be similar to Ness, but with more air acceleration. this would make frisk easy to weave in and out and avoid attacks. They have 1 standard double jump.
However, when LOVE gets higher, air acceleration gets worse, and dash turnaround takes longer, making it easy to keep running in, but punishable if you run away. LOVE also reduces the invulnerability on dodges.
Weight would be average, at about 94. (similar to ness or inkling)
It doesn't seem that there is any long term benefits to being either a Pacifist or a Killer. I feel people will be more inclined to try and stay neutral as possible. Being a Pacifist is too difficult to reach with the limited movesets that lowers your LV. Being a Killer slows down your mobility and dodging which will more or less get annoying to deal with because you will feel as you're being punished for playing the game.
I know you're limiting the movement speed and dodging from Genocide mode to discourage players from going the genocide route but not only does that again punish players for playing the game properly, it also doesn't make sense in the games because there is no reduced movement speed in a genocide run.
Special Moves:
Up B- Bird That Carries You Over A Disproportionately Small Gap
Similar to one of megaman's custom moves in smash 4, a bird will fly to frisk's hands and grab him, flying him straight up, with some variance in exact angle. no hitbox, standard recovery.
if your LOVE is too high, the bird won't want to help, not lifting as much. at 75-99% LOVE, the bird has a chance to not appear at all. at 100% LOVE, the bird will not show up, and this move will be about as good for recovery as Yoshi's up b, forcing you to rely on your double jump for recovery.
This is a move that punishes you for playing Smash Bros properly. No other character limits your options for attacking the opponent and from your idea of LV gained based on damage, it can be too easy to get high LV and then lose because you were playing too good. Couple that with the mobility loss from the Genocide mode effectively makes you worthless at recovering.
The Genocide mode should have a different method of recovering.
Side B- Shank
Frisk will use a knife, differing depending on how full LOVE meter is, and do a very short-range powerful attack that drastically scales with LOVE. this attack has a crumple effect similar to Ryu or Ridley's down b.
-at 0%-25% LOVE, they will use the toy knife, very little damage but enough hitstun to be positive on-hit
-at 26-75% LOVE, they will use the worn dagger, which deals decent damage (20-30%) and enough hitstun for a followup
-at 76%-100% LOVE, they will use the real knife, which can deal up to 50% damage, but not enough hitstun for a true followup (tech chase)
A good move that rewards pacifism, neutral and genocide forms. Not much else to say about it.
Down B- Spare
Frisk will try to hug the enemy, a command grab attack similar to Wario's bite. It can't be shielded.
Using this move, whether it hits or not, will lower your LOVE by 20%, but the more LOVE you have, the longer this move takes. Whiffing this move is likely to get you hit by a smash attack.
Damage dealt by this move will NOT fill up your LOVE meter.
-at 0% LOVE, this move will remove a stock from any opponent above 130%. (similar to some final smashes) Otherwise, it deals around 30% and has very high knockback that may kill before 130% near the ledge.
-at 1%-99% LOVE, it deals damage equal to about half of your LOVE and removes all of it (if it hits)
-at 100% LOVE, should this move actually hit your opponent, you get dunked on and lose a stock. With how slow the move is, your opponent can likely react and get hit on purpose to kill you.
LV 0 seems like a nice reward for being a pacifist with how difficult it is to be one. However being at LV 100 with this move seems pointless because you can lose all of your LV by being KO'd or simply self destructing and there doesn't seem to be any reason to use this move at that point. It's better to just keep at it until you're eventually KO'd. I know where you're going with this but the move should be replaced with something else when your at LV 100 that benefits Genocide mode.
Neutral B- SAVE
If you don't want to risk using spare to get rid of your LOVE, you have another option.
SAVE will fill frisk with determination, and slowly drain their LOVE, Similar to Cloud's down b. Using down b to get rid of LOVE is slightly faster, but this option is much less risky.
However, at 100% LOVE, this move will not reduce your meter. Instead, it will heal you very slowly. This is to make it a lot harder to lose your LOVE if you reach 100%, as you’re forced to use down b.
It seems like Genocide Frisk will act as more of a tank with the movement speed and dodging reduced but could end up being very easy to combo.
Overall I think this moveset is a little too complicated and at a lot of times hinders the player for playing the game normally. I think a good moveset is one that keeps things simple, works with Smash Bros and stays true to the games as much as possible. If something doesn't work or makes things complicated, think of something else that will work better.
The idea of having multiple attacks for all three alignments seems like it would take a lot of work and balancing to have the character ready for Smash. Then again, the pacifist/genocide mechanic of the Undertale games should be a crucial part to staying true to the game the character appears in.
I'll try and come up with a moveset for Frisk and see if I can try and make Frisk work, despite if I think they have no moveset potential. I'll post it to the Frisk thread since I'm deviating well away from Geno with this.