Preta path - Obito could do wood release great spear tree, wood release underground roots technique, wood release cutting technique and fire release phoenix sage fire technique ( with shurikens hiding inside the flames).
Obito's use of Mokuton was severely limited on its own, as seen as he barely uses it without a proxy to boost his power.
Wood Release: Cutting Technique is used in two instances by Obito that I can remember, the first being when he was inside GuruGuru which greatly boosted his powers. The second was when he was connected to the Juubi and channeled the attack through it, at which point he was also connected to Madara. He never uses this technique outside of these scenarios, meaning that even if he could do that it would likely be severely weaker.
The same can be said about
Wood Release: Great Spear Tree, which was also only being use alongside GuruGuru. I also don't recall when he used
Wood Release: Underground Roots Technique but I assume it was when he used Mokuton to grab unto Naruto during the war or when he fought with GuruGuru in his childhood. GuruGuru really isn't a valid case as he was severely helped in that scenario and doesn't possess such power himself. The way he used Wood Style against Naruto wouldn't even be useful against Pain as he would have to get both into melee range and use a slow moving technique against a single path, locking both of them down.
Fire Release: Phoenix Sage Fire Technique was only ever used by Obito in filler content and while I have no doubt in my heart that he can use it as he is an Uchiha, then it would just be absorbed by Preta Path regardless.
Animal path - Obito will probably have to pull out the chakra receivers and use wood release to pull the big chakra receivers out, then use Kamui to not get hit by any of the pains or use Zetsu to distract the pains. Obito can also use the demonic statue chains to temporarily stop the summons (I am not 100% he can do this tho). Or use Kamui to take the animal path into the other dimension and when he summons, Obito can use Kamui to phase into the animals and go right after the pain.
You are overestimating the capabilities of Kamui too much. Obito cannot cast Ninjutsu, Genjutsu or Taijutsu while casting Kamui if the technique is physical or requires hand seals. He was only ever shown to be able to cast Visual Based Techniques like Izanagi. The only one who could cast both Kamui and attack at the same time was Kakashi when he possessed both the Mangekyou Sharingan and Obito's Rikudou Chakra, which isn't the Obito who we are debating in this conversation and we don't know the capabilities of having both of them.
That means even if he get close to a Pain he needs to turn off his Kamui to attack, which is why he was unable to beat Kakashi, Gai, Killer Bee and Naruto as they exploited this opening to attack him. With the knowledge that Konan possessed a great understanding of Kamui then I'd say its rather safe to assume that Nagato also had this knowledge from working with Obito for years. Meaning he would know how to counter Kamui and likely know about the time limit it has. Obito's Paths had a single Chakra Reciever in order to control them, the Pain's had several.
Meaning he couldn't just "pull" them out in the heat of a battle where as Pain could stop Obito's Paths by pulling them out as Naruto and Killer Bee did. As outlined above, Mokuton wouldn't do much for Obito other than leaving him open for an attack. Obito would also not be able to use the Gedo Statue in any way or shape as both Nagato and Obito can control it, hence the other would just cancel it out. The only other application of using this as far as we know is to connect it to a black rod that Obito has created himself, as it needs to be tied to his chakra.
Also if Obito would have to resort to using Zetsu then he already admits defeat as the fight would no longer be 1v1, but 2v1.
Asura path - wood release techniques under him, Zetsu to distract again coming under him and maybe even damage him a little or explosive landmines to blow him and the other paths up.
Obito's Mokuton wouldn't do much as stated above, Zetsu would be cheating and Landmines would just be deflected by Tendo Path or avoided as Pain would be able to see their location with Rinnegan, if not just move away from the field. The reason Sasuke didn't do that with Deidara was that Deidara was flying above it, something Obito cannot do. If Sasuke wanted to retread then Deidara would need to follow him if he wanted to fight him.
Deva path - fire release phoenix sage fire technique (with shurikens hiding inside the flames). Earth release hiding like a mole technique and go under pain and using the demonic statue chains to make him not move.
Fire Release: Phoenix Sage Fire Technique was again only ever used in the anime and not in the manga, but even then a single
Shinra Tensei would stop the Fire Chakra and the Shuriken in their tracks.
Earth Release: Hiding Like a Mole Technique wouldn't serve a purpose against Pain as he could detect your chakra with Rinnegan and act accordingly. Beyond that Obito can't combine it with Kamui, hence the instant he gets close to a Pain they would move out of the way unless it was Tendo, at which point a
Shinra Tensei would just be used.
Human path - The human path is (in my opinion) the weakest path of them all. Only because of the fact that the user needs to have their hand right over the target’s head to take there soul. So Obito could just avoid it and in a 1v1 situation, it will be fairly easy to kill (see down below how that could happen). But if the other pains were there too he would be protected and if the other pains were about to get killed he would just go in front of them and sacrifice himself.
People tend to underestimate the Human Path greatly. If he gets a hold of you, you are dead. Human Path's fighting style is a lot like Obito's use of Kamui. Meaning in a fight between these two it would be about who can touch the other first and even if Obito was successfully then he would put himself at immense risk. We know that Obito takes a few seconds to "absorb" and transport you with Kamui at which point Human Path can grab his soul. At this point Obito has two options;
- Either he transports Human Path who is holding unto his own soul, splitting his soul away from his body and killing himself.
- That doesn't work and because the soul is out of his body he can no longer use Kamui to go between dimensions.
The final one is the more likely judging by his limitations with Kamui as seen when he absorbed the Juubi.
Naraka path - The Naraka path’s first ability is easy to avoid because of the fact that Obito has Kamui. The second ability is really hard to do anything about, but Obito needs to get close to the Naraka path and use Kamui to take him into the other dimension and by doing so the other pains cant be fully repaired after taking a lot of damage. After that Obito just has to fight the Naraka path without being touched once, like i said pretty easy for Obito.
I'll address a point of yours you seem very keen to bring out and that is "Obito could just Kamui a Path to another dimension" which is unlikely. Pain had shared vision and made it a habit to keep a path in his eyesight at all times. The only times he was caught off guard was when he was ambushed or when he put his guard down. The instant Obito went out of Kamui to grab a Pain he would know it and would just respond with Tendo's
Universal Pull or move the Pain out of the way and attack with the other Pains.
Any damage that Obito takes by a jutsu that involves a hand seal will be regenerated because of hashirama’s DNA. I don't know if summoning jutsu counts but just for the sake of it I won't count it
Obito can
only regenerate the tissue that was replaced with Zetsu DNA quickly, his normal body doesn't heal quickly as seen with his scars and long healing time in Madara's cave.
Obito could use Kamui on every pain and finish them off in that dimension (without the other pains interference) He does need to get close to them first which might be a problem but could use some Jutsus listed above to achieve this. Fx Kamui to not get attacked by the pains and then go over to whichever pain he wants to get rid of first (I would probably say the Naraka path because of the fact that it can heal the other pains).
As mentioned earlier, the instance Obito deactivates Kamui he can be grabbed by Tendo's
Universal Pull or ganged by the other Pains. Even Naruto was unable to get around this and was only given a shot because he didn't have to worry about Tendo, ambushed one of them and was lucky enough for Pain not to notice the Senjutsu being absorbed by Preta quick enough. The instant Tendo came online again, Naruto lost the fight.