Hiruzen can start of the fight by sending one or two kage bunshins to attack Deidara while he summons Enma and observes Deidara's initial movements. Orochimaru implied that Hiruzen's fighting style revolved around them [
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] while using his keen intellectual capacity to figure out the fighting style and the subtle intricacies/nature of the opponent's attacks as shown in the war arc [
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]-[
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]
The clone or clones' large AoE kage shuriken whether in
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or in
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form should pressure Deidara into retaliating by jumping and prepping a clay bird. The C2 Dragon is very bulky and its flight pattern is laboured compared to his smaller birds, and it wasn't even capable of dodging Chidori Spear's
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. The small bird is very agile but Deidara's attacks aren't as powerful without access to his C2 bombs. Given the fact that the clones can follow up a kage shuriken with a large scale Fire and Wind Release combination that arguably spans the entire width of a bijuu [
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], Deidara should opt to form his smaller bird to start out the match to evade some techniques rather than risk getting shot out of the sky immediately. We've also seen that, in the manga, Deidara's natural progression is from C1 to his stronger attacks like C2 and either C3 or C4 both of which he doesn't use unless it's neccessary for him to do so. Not to mention that the C2 bird makes Deidara a bigger target.
After Deidara attains flight, he'll start with some standard C1 bombs to dispatch the clones in pursuit of him, but the C1 can be tanked by spitting out thick earth walls. C1 was
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. Hiruzen's chakra is obviously much stronger than Akatsuchi's and he is also capable of making larger and thicker earth walls in comparison. The real Hiruzen can either form an earth wall beneath him or spit mud at the ground beneath him and use the material to create an earth wall while he stands on top of it to elevate himself and get closer to Deidara in the air. The already sizable wall used by Hiruzen in part one [
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] should be scaled up since he now has a much greater capacity to mould and release chakra as an Edo, as if he were in his prime.
The adamantine staff extension and some giant lightning spears used by the kage bunshins below, and/or the bunshin the real Hiruzen can form to his side should give Deidara one hell of a time as it's much tougher to dodge large scale attacks from different directions. Kage fūma shuriken imbued with Lightning Release should overwhelm and diffuse the amount of bombs Deidara can create at a time. Don't discount Hiruzen from doing this at all as he will know that Deidara is from Iwagakure, and a large number of their shinobi have the Earth Release affinity. He was also capable of figuring out the Gudōdama's properties through mere observation and combat.
Another point to consider is the speed of Hiruzen's execution and jutsus. He was able to meet the Buddha's natures halfway despite SZ having shot them first. Also, they only take one hand seal.
Hiruzen wins mid difficulty.