Sasori is one of my favorite characters but I have to give this to Oro because,
Hiruko: Hiruko is hard but Oro has shown many techniques capable of breaking something of that level including his Kusanagi, he has his needles but Oro is a Sanin who has fought hundreds of battles if not thousands and has most definitely fought a puppet user before and could most likely dodge those with ease, Hiruko has his tail which seems half useless since it couldn't even stop Sakura a ninja with less than a tenth of Oro's skill and knowledge therefore Hiruko gone almost instantly with no damage whatsoever to Oro.
3rd Kazekage: the Iron Sand technique has a weakness in a huge open area like the field the OP put them in, the weakness is that unlike the cave where he fought Sakura and Chiyo Oro could just back out of range. The puppet just needs to be destroyed to get rid of his annoying technique and Oro could Rashoman and go underground,(still Rashoman) or summon Manda and fight while Manda waits underground for a chance to strike etc. many plans for someone of his intelligence and knowledge.
100 puppets: Sakura was dodging around and destroying these puppets....... that means Oro will clean them up in seconds( I really never understood the power of these puppets since Chiyo with 10 puppets and a Sakura could devastate them all), someone above said he could use 100 techs at once, that would take all his thought processes since he would have to think of them all at the same time and then aim them and fire while controlling all 100 puppets, that would take time and push his mind away from Oro who could just make a clone and stab him through his heart tube in the meantime.
Sasori himself: He has rotating blades which won't hurt the ever ressurecting Oro and a flamethrower which has the same drawback, and a rope spear-same, and...... I think that's all he showed
Oro has a poison immunity to most types of poison, which doesn't necessarily mean he is immune to Sasori's, which means he is at the very least resistant to virtually any poison since 99% of poisons have actively recurring traits that are shared by just about anything that is poisonous in any way which means Oro's immunity to most poisons makes him far from weak against any possible combination of poisons Sasori could possibly make
Some Imbecile said that Sasori could control Oro with chakra strings..? WTF Chiyo could control Sakura because she was alowed to, if you honestly believe that a tiny string made of chakra can control a high level ninja if they don't want it to, you sir are around the same level as a retarded maggot who was dropped on their head repeatedly from a vast height which it survived only by using its brain as a cushion.