With his many sensory options, followed the movements of Guru and his statue to perfection. The Yondaime would notice the sudden substitution, and then the ascent into the air, following every detail and no his poison wouldn't effect himself. He would then notice the large amount of chakra flowing through the sky, only to be suddenly greeted with the all too common occurrence of rain. Seeing as the Yondaime was in a Senjutsu enhanced Susanoo, a deity in which he could indefinitely pump chakra into to extend it further than normal, he was not too worried. But that was when it was a drizzle, once it became a downpour that was another story.
The Yondaime would utilize his Susanoo's shield as an extra buff to buy him more time as he watched his ethereal warrior got blasted with the acidic rain, a nice twist the Yondaime thought to himself. While the Yondaime was fairly certain he could keep his defense up and not be assaulted, why risk it? Thus in a purple flash, his Susanoo and him disappeared. As stated earlier, the Yondaime had flung a hiraishin marked kunai far away from the battlefield. One could argue this was still in proximity to the rain, except he noted it being away from the field of action. Plus a wind coated kunai, launched by senjutsu enhanced strength, from a high position, would travel quite the distance before it eventually fell to the floor. Thus the Yondaime and his Susanoo which was connected to him via chakra would teleport outside the poison fog and acidic rain.
While the rain might eventually clear his field of poison, it would not do so instantly. Meaning if his foe only relied on the sharingan, this set of actions would remain hidden to him. Guru would be unaware that the Yondaime would have left the zone and the Yondaime was probably too far away to even see, it wasn't the byakugan after all. This wouldn't last long however, as the Yondaime would make his appearance very known soon.
Quickly weaving through five kata, the zone itself would be filled with the essence of the Yondaime's chakra. A fact Guru would likely be able to see, though not pinpoint its exact location. A strong hurricane like wind would blow into the area, causing a massive gust of wind to sweep over the area. The Yondaime at first would the wind start from gently behind him, if only to blow off the excess acid on his Susanoo. After that, however, it would affect everything in front of him, and rage like a storm. No it wouldn't topple trees and cause such havoc, although it could possibly blow Guru off his statue if the creature was careless.
The main point in said wind was to clear the battlefield and start fresh. The Yondaime's dokuton would be blown away, but so too would his enemies clouds. Since it was invisible non-solid wind, the santon would have nothing to dissolve, unless it suddenly dissolved air molecules and currents moving about. Even if the acidic rain could stop the wind, the Yondaime with his infinite chakra could keep it going longer, than Guru could fight back for. Combined with his unlimited tank of chakra, and his acid not destroying things instantly, and some of the wind affected the acid couldn't reach (Above and to the side of the cloud) Guru's clouds like any bad storm would eventually blow away. No, they wouldn't be dispersed, but they wouldn't be in the area even remotely. The Yondaime would not let up and continue this massive gust of wind indefinitely, clearing the battlefield and potentially blowing Guru about. If not for being an Edo Tensei, and being a Sage, such a high scale massive gust would not have been possible.
The only downside was that the Yondaime would clear the field, making himself much easier to spot. Thus the Yondaime would simultaneously send chakra out to repair his damaged bit of Susanoo, in anticipation of a counter.
1. Hiraishin
2. Wind Release: Great Breakthrough (Large Scale Variant)