It appears, with Cell being able to break through Zamasu's immortality, the fight would be a bit fair.
Vegeta was almost done recovering from his wounds, and if he needs to jump in immediately, Cell decided to bring along a few of those Senzu Beans. Trunks was starting to get back to his feet, intending to assist Goku once more.
Goku and Black were still going at it. Black was a little stronger, but of course, Goku had more experience using his own body, so when they both used their full strength, they were rather equal.
Anyways, back to Cell. He is currently absolutely destroying Zamasu. Like Belly with Frieza, kind of. Cell would kill him, but thought, why not keep him up for a little bit? It's a free punching bag. But, that may be a bad decision. Oh well, it's his to make.
Anyways, due to the Zenkais, Black surpassed Goku completely, and immediately knocks him unconscious, down beside the Time Machine.
Then, with Black and Zamasu as a duo again, they go up against Vegeta, Cell, and Trunks. At first, due to Vegeta's determination to win, Cell being the strongest good guy there except Goku, and Trunks being a good support, they did rather well. But again, Black somehow keeps getting stronger, and so soon enough, they're all down beside Goku. Except Cell. He has the most stamina, and potential, out of everyone fighting at the moment. He noticed Trunks was still conscious, and so threw him the bag of Senzus he was carrying around.
"Get them each Senzu Beans, throw them in the Time Machine, and send them off.. We're not leaving until these two are nothing but ashes.."
Trunks wants to go against this. But he knows Cell is stronger than him, so he obeys. Cell put 6 Senzu Beans in the bag, so after giving Goku and Vegeta one each, then taking them out of the fight, Cell and Trunks could each have two.
After they both use up one, Trunks gets a Zenkai, because he's in far worse shape. With this, he takes on Zamasu. Cell gets another shot at Black, this time, using his speed, techniques, and brilliant fighting mind to his advantage, which was the right call. Once Black starts running out of stamina, even though he's constantly gaining strength, Cell keeps the upper hand.
Until, Zamasu takes care of Trunks, and the two team up on the Bio Creature. In fact, they defeat him with one giant blast.. Zamasu feels like he's not really dead. But he decides to ignore this feeling. Trunks slowly gets up, as his power begins growing rapidly.. Yup, it's Super Saiyan Rage time. He does well against them, since both "Gods" have been weakened or worn out by Cell, and Trunks had a Zenkai due to the Senzu. And, the moment the Future Warrior begins getting overwhelmed again, in fact, Black was about to land the killing blow- They all feel a massive power, and stop fighting. A cloud of dust and dirt covers up where that power is coming from. Black says, with a concerned tone in his voice-
"That's.. That's not him. Is it?"
Zamasu replies-
"I'm afraid it is, my friend.."
Now, this wasn't a normal Zenkai, like he got after Self Destruction. His nucleus absorbed the radiation that the Blast Goku Black and Zamasu used to "kill" him left over, And, being furious once he has regenerated, ends up waking up a slightly dormant power.
Cell's aura was a filled in Gold, with Purple and Red sometimes appearing in it. His eyes were crimson. But after that, no physical difference is seen. But it is obvious. This is like a halfway point between Base and Frieza's Golden Form.
Oh, and yes, this is a transformation, not a permanent thing. Cell really just activated it by accident. Or maybe, something forced him to activate it. Perhaps, Frieza's still with us, just not in a physical form.
Anyways, "Golden Omen" Cell and SS Rage Trunks start taking on the two gods. And they do good. In fact, a little too good. As Trunks holds back Zamasu, Cell doesn't even give Black a chance. By the time Cell is done beating him to a pulp, His own blood is all over him, as well as on Cell's fists. And the Bug Man has nothing to say. He simply gives Black a deadly stare that the Counterfeit Saiyan will always remember. No more quips or smartass comments, Cell is done playing around with these bastards. Wanting to be gods so badly, that they think they actually are ones.
But, the two aren't finished yet. The two move around their strange earrings a bit, and as they glow, begin to move towards eachother. Remember, Potara Fusion has never been seen before in this timeline.
Cell feels the frightening power the two end up making when they merge. Originally, Merged Zamasu was going to be as strong as Two Super Saiyan Blues. But here, Black is a hell of a lot stronger. So not only is Merged Zamasu stronger, but Black holds the dominance over the form. This Merged Zamasu is like the one Goku fought Head-On in the Manga. But, Cell wasn't scared. Not at all. He felt.. a bit of joy. Forming a grin on his face, As he and the Merged Zamasu look into eachother's eyes. Cell says one more thing.
"Finally.. A challenge."