Even if Discord DID lead with it, how strong is his Existence Erasure?
Immortality (Types 1, 3, 7, and 8. Hair Ball users should be capable of living forever and boasting no lifespan, along with being able to lose their whole body, mind, and soul, and still be alive. Bo-bobo has killed the Demon King and everyone in Hell, and can come back from any afterlife. Bo-bobo has been both a vampire and a zombie before, and his Type 8 is due to being reliant on his Hair Soul, which can survive even if his body, mind, and soul are completely erased)
So, where is Bobobo's Hair Ball (Which holds his Hair Soul) normally, how can Discord know about it, let alone know he needs to get rid of it, & how does he get rid of it?
In any case, their personality clashing is interesting. Bobobo may act ridiculous, but it's as a strategy to confound their opponent into submission.... And the absurdity is stuff Discord would just find it hilarious.
But on the other hand, I don't recall Bobobo laughing, nor showing amusement much, which Discord would find annoying, or a challenge. (Willingness to kill aside.)
Even without that, Bobobo has Resistance to Petrification, Wind Manipulation, Paralysis Inducement, Mind Control, Sealing, Dream Manipulation, Transmutation, & Possession.
Also, Telepathy (Depending on use), Information Analysis & Instinctive Precognition may help. (Although, Instinctive Precognition to predict Discord, the embodiment of Chaos, who's probably naturally unpredictable, might not help as much.) And Probability Manipulation.
Bobobo is a challenge to defeat. The only thing MIGHT be BFR (In part because he only has Interstellar Range, presumably for Teleportation, and Portal Creation is in one of Bobobo's higher keys.) Not sure if Bobobo's Resistance to Sealing is relevant.
If he is killed, Resurrection helps. Cloning might also help if Discord only BFRs one at a time, and he might try that too late.
Both of them have Power Nullification. Both also have Time Travel, but Bobobo is for appearing in a story 1,000 years in the past; He might use it for absurdity, not as a tactic.
Discord's issue seems like he might not try BFR first.
Discord's Intangibility might not help, because of Bobobo's Soul Manipulation, Death Manipulation.
Besides that, Bobobo's Conceptual Manipulation (Which might be too limited to help) is another win condition. Transmutation, too, since, wasn't Discord inactive for a while after being Petrified?
Also, I don't know the exact values they're scaled to (If they're present, but....)
Attack Potency: At least Star level (Defeated both Celestia and Luna at once with ease, who themselves can raise the Sun and Moon with immense ease. Is possibly the one responsible for creating his own realm. Said to be able to defeat the whole changeling army with just a sneeze. Stronger than King Sombra)
Attack Potency: At least Large Star level (Is able to hurt the Three Civilizations who could take attacks from Bobopatchnosuke before Majide Time. Moved a background full of stars across the sky when turning it to night time. Funny Sugoroku is a pocket reality made by Bo-bobo that had a background full of stars)
The difference between baseline and maximum Star Level is ~5.59x and for Large Star Level, it's ~715.59x .
So, how hard Bobobo smacks Discord (Even if he thinks to go Intangible, he has several forms of Elemental Manipulation, which might work.) depends on how far into their tiers they are.
Overall, I think Bobobo has slightly more win conditions, resists several of Discord's, has several powers that help him avoid being exposed to Discord's powers or to learn how to fight Discord (which, going by Bobobo's intelligence section, he's actually VERY good at.), & Discord has to resort to one specific one, which he might not do first, since he wouldn't initially know to do so.
Not only that, Discord is often casual, underestimates foes, & would laugh at & enjoy Bobobo's natural strategy of trying to confuse & freak out his opponent; Discord would probably find Bobobo entertaining, likely making him reluctant to end the fight, or willing to prolong it.
But Bobobo would see a challenge, puzzle, or reason to try much harder at Discord, and might just bust out his win conditions sooner, instead of goofing around as much as normal.
CinnabarManx421 wrote: Discord, he starts with Power null in character so he would just take away all of Bobobo's powers immediately. Voting Discord.
Problem is, Discord would have to know about Bobobo's source of power (his hairball) in order to nullify it. Discord's power null seems to depend on removing the opponent's power source, as was the case with removing Twilight and Rarity's horns and Fluttershy and Rainbow Dash's wings. I doubt his power null could work if he doesn't know about Bobobo's hairball.
When Discord Power Nullified the Mane 6, that was in his first appearance in Season 2, before his character development. Besides that:
1. Before everyone had gotten to the maze where the Mane 6 where, he was asked about where the Elements were, which was why he invited them to the maze. (Nevermind all the goofing around he did BEFORE being confronted when he could've conquered Equestria.)
2. The Power Nullification was part of a game to ensure they didn't cheat with flight or magic in the maze.
His game plan once they were ACTUALLY in the maze was to Mind Manipulate or corrupt them. But he doesn't know this opponent resists those. It's likely he could just waste time trying those without Power Nullifying first.
3. Information Analysis, "InstinctivePrecognition" (As Bobobo's profile puts it), Teleportation, Plot Manipulation, & to a lesser extent, Duplication & Time Travel make much harder to actually LAND Power Nullification, especially if Discord's not serious to begin with (Which is made worse by his foe's entertainingly weird to him.) Heck, Bobobo himself has Power Nullification.
4. If his Power Nullification was done by taking away horns & wings, it runs into the issue that it may only be on a biological level. If he kills Bobobo, or gets rid of him in any way that Bobobo's Hair Ball can bring him back from, it's questionable if Bobobo will still have his powers negated, since he'd come back whole.
Not to mention, the Hair Ball is NOT Bobobo's afro, nor is it in a very immediately obvious place.
Hair Ball - Bo-bobo's essence is called the Hair Ball, and according to Tsuru Tsururina III, is the source of power within a Hair Citizen. It holds a separate soul from their normal one, their Hair Soul, which can't be accessed normally through regular soul-based attacks, as well as their essence and their "life". It makes Bo-bobo so hard to "kill", as one needs to destroy this to fully kill him, and even erasing his mind, body, and soul completely will not defeat him while his Hair Ball still exists.
Given that Discord isn't trying to set up a maze game with no cheating here, & how, when he was trying to conquer Equestria, he was causing Chaos, & when asked where the elements were, challenged his foes to a game, waited for them to show up so he could Mind Manipulate/Corrupt, instead of Power Nulling immediately....
Not to mention if his motive to Power Null was to stop cheating & Discord is noted as having a weakness of underestimating foes, Bobobo being likely to seem entertainingly chaotic (His go-to strategy is to try to confuse his opponents.), Discord might hesitate to go all out at first.
Given all that, I don't think Power Null is quite Discord's opening move, & he still has several things he could try first he doesn't know Bobobo resists.
And killing/erasing Bobobo makes him come back.
And Bobobo, at least going his profile, has better intelligence, & more skill & experience in combat, with a variety of abilities that make it difficult to actually land a Power Nullification that's based on removing anatomy in the first place.
I'm keeping on my vote on Bobobo. I don't think Power Null in the way & effectiveness Discord uses it is enough to compensate against Bobobo's intelligence, abilities, & skill.