@Nerx: Comparing Gaara's "Undefeated" status to Pain's isn't a plausible argument at all considering that Pain has defeated immensely powerful shinobi unlike Gaara, Gaara has never faced anyone with the power that Hanzo possessed. Secondly most of Deidara's attacks can easily be repelled by the Deva Path's Bansho Ten'in regardless of the fact that he cannot use it in rapid succession, the waiting period is still very short being a few seconds. Regardless of the fact that Deidara has never faced Jiraiya it is ridiculously clear that he cannot defeat him, even Itachi with Kisame to aid him was scared of fighting Jiraiya aware of the power he possessed and Pain in turn easily defeat his former master. Pain's Animal Path can summon countless creatures into battle at rapid succession, and Deidara using his explosives to deal with the beasts would not be an effective way of defeating them considering that Pain possesses an incredibly high amount of chakra that would allow him to summon an overwhelming number of summons. Deidara struggled against Gaara, I do not think he would even remotely pose a challenge or threat to Pain, Deidara would have to rely on long ranged attacks that Pain can protect himself against or dodge, if Deidara were to get in close range he would fall under the control of Pain's Rinnegan allowing Pain to pierce him with a chakra rod to either kill him or gain 100% control over Deidara. A Chibaku Tensei does not take long to charge, using a Chibaku Tensei would ensure Pain's victory even further.
It should also be noted that Pain was so immensely powerful that Sage Mode Jiraiya (an opponent even Itachi feared fighting) was unable to defeat him, and his power was so that he forced a Six-Tailed Naruto to resort to his Eight-Tailed Form to break his Chibaku Tensei and even more so Naruto nearly freed the Nine Tailed Demon Fox simply because he had lost hope of defeating Pain due to his unimaginable power. Pain would be able to repel Deidara's explosives with his Bansho Ten'in, his "Six Paths Of Pain" should provide an overwhelming offensive attack, the numbers game would overwhelm Deidara, Pain's "Outer Path" is able to revive any one of Pain's bodies if damaged as demonstrated when it revived the Asura Path even restoring its Akatsuki cloak. Pain's Animal Path can simply summon a gigantic bird for his Preta Path to use to get in close range to Deidara and absorb his chakra and so that Deidara isn't aware of the Preta Path's approach, the Animal Path can simply summon another creature into battle to distract Deidara while the Preta Path ambushes and absorbs Deidara's chakra. The Preta Path is able to absorb any ninjutsu-related technique thereby nullifying them, the Preta Path was also shown to have a barrier around its body that absorbs any attack, the only attacks it was shown to be vulnerable to were "physical ones such as punches".
Pain's Asura Path is capable of firing a cluster of segmented missiles at its target. The Asura Path possessed sufficient physical power to rip off one of Sage Jiraiya's arms and crush his throat using merely taijutsu, it was also physically strong enough to toss the Animal Path all the way into central Konoha from the forests in the outskirts. The Asura Path was quite fast being able to propel itself with a quick burst of chakra from its boots, it could protract countless blades and drills in battle to easily slice its opponent. Its most powerful ability: The Asura Path could open up its head and release a colossal shockwave of titanic proportions capable of destroying numerous buildings at once. The Asura Path possesses a highly versatile set of abilities and it can be used as a human shield for the other bodies as evidenced when it readily took Kakashi's Lightning Cutter in order to protect Pain's God Realm (The Deva Path) however it was brought back to life by the Outer Path.
ND