Hidden Conditions:
For the hidden condition, you have to defeat Piccolo and Goku first before Gohan. This can be quite tough especially when your allies fall. You have to bring an All-Energy Capsule to ensure that their health is up. For the first, you just need to knock out Hercule. Then, Tien, Krillin, and Yamcha will arrive. They can be a pain if you'll just rely on combos; surprisingly, powerful Ki Blasts is effective against them. After taking them out, the difficulty will be nudged a little since you'll be fighting the father-son tandem of Super Saiyan Vegeta and (Future) Trunks. These two work very well in coordinated attacks so you have to watch your back.
Finally, after taking the two out, make sure to use recovery items as necessary since Piccolo, SS Goku, and SS Gohan will arrive. Piccolo should be the easiest to take out of the three. Get rid of him immediately to give your team breathing space. Next, try to take out Goku as fast as you can. He's quite stubborn and hard to stagger. He likes to use Evasive Skills frequently as well.
After managing to defeat SS Goku, Gohan will be enraged and will become a Super Saiyan 2. At the same time, Perfect Cell will arrive as an ally. Gang up on the powered-up Gohan and defeat him to complete the mission.
I absolutly hate this level!! Krillin and tien always gan up on me and my allies focus on yamcha for some reason. Maddening
Did this at least 100 times, cant get ss2 no matter what. A d naturally when cell jumps in, gohan jumps on him and takes him out with one freaking blast. It is impossible.
Above description is good, but please note that at different stages random chances occur. Whether or not gohan goes SSJ2 after goku/piccolo dies is random; once goes DOES go SSJ 2, it's random whether or not cell (perfect) jumps in; and once cell (perfect) does jump in the fight against SSJ2 gohan, and you win the match, its random whether or not you get the SSJ2 drop. You have to ultimate finish the quest succeeding in all random chances to get the SSJ2 skill