Who is more powerful individually,a old god or a titan?
Well that depends a lot on who the titan is, if it is someone of minor rank then I can't possibly justify that Titan to be more powerful than Yogg-Saron or C'Thun. If we open the debate up however and say Sargeras vs C'Thun then that becomes difficult. I would still however say C'Thun. I say C'Thun since he was clearly able to fool even the most powerful of the titans that he was dead. It was also strongly hinted that he in a 1 on 1 with a titan slew said titan.
What makes the question the most difficult is that we only know the identity of 4/5 Old Gods. In the third War of the Ancients book which came out shortly prior to Ahn'Qiraj the aspects said that to their knowledge 3 Old Gods remained alive. Y'shaarj was not one of these for obvious reasons but also not C'Thun since at the time of War of the Ancients the world still thought him to be dead. So when the Aspects said that to their knowledge three old gods remained alive they meant Yogg-Saron, N'Zoth and a third unknown Old God.
Name 10 characters who played a role in WoTA
What is the name and race of the first mortal to harm Sargeras?
On what part of Sargeras' body did he harm him?
How did he reach Sargeras?
I'm going to leave the yellow and green for others to solve.
1. Lord Ravencrest, Tyrande, Illidan, Malfurion, Jarod, Shandris, Azshara, Broxigar, Rhonin, Krasus, Alexstrasza, Ysera, Neltharion, Malygos, Nozdurmo, Soridormi, Tyranstrasz, Cenarius, Hakkar, Archimonde, Mannoroth and Sargeras. (A bit more than 10.

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2. Broxigar, orc. And to my knowledge he's not only the first but the only one. Unless you account for Aegwynn who really only fought his avatar.
3. His leg? (Not 100% on that one, but I think it was his leg)
4. He jumped through the portal designed to summon Sargeras into Azeroth, managing to buy the heroes of our time to stop Sargeras from ever entering it. Once there he used his axe forged by Malfurion under the guide of Cenarius, an axe made only from wood but far sharper than any steel.