After the closing episode of the Transformers Prime season 2, they got the other option on how to reincarnated the certainly death Optimus Prime for the season 3 opening.They can choose the good side of the stories which Prime meet their good god in the Well Of The All Spark ,Primus i(which they did) or make a deal with the Devil God itself Unicron inside earth belly just like in the picture above.
So this is the stories that they give us in the season 3 opening, the beast prime Optimus Prime. too good and clean way to reincarnated the Prime with the help of the hammer of the Soulless Prime.
But the evil dark side stories is never been told. only the toys is released by the Japanese gang.This is still the clean version of the dark side. The more appropriate to get the black, dark and grey version of both of the character(still hunting).So in this stories, during the nearly death prime waiting his death in the underground of the earth, Unicron itself who Optimus kept him prisoner inside the earth came approaching him and offer him a deal to destroy megatron who betray him by trying to kill him.
At this side of the stories, Optimus agreed to Unicron proposal and make deal with the devil himself. So Optimus prime healed by the Unicron Evil power
and give him a snake tattoo a symbol of evil Unicron. This is my fifth version of this optimus prime.
So this is how Unicron reemerging itself on Earth to Optimus Prime. Almost resemblance with one of the Thor movie character which is the guardian who guard the Asgard Gate.
At the back you can see the evil Unicron head as his back eyes. so nobody can attack, stab him from the back.
So they deal is not just to heal Optimus prime only, but also make Unicron available inside optimus prime.
So the only way to make it happen is that they have to combine.
Since that Unicron itself doesn't have it own body, combining with optimus prime can make him and optimus more powerfull and stronger.
Feel hard for Optimus to except it but if this is the only way to defeat megatron.If this is the side of the story happen. Megatron definitely be death. Even if Optimus still have mercy to spare Megatron, I don't think Unicron have any mercy.
So that just the story goes. If this is the story, they gonna have problem with rest of the season. how will Optimus betray Unicron? Will Megatron seek help from the good god Unicron for upgrade him to Galvatron? Who is autobot and who is decepticon? So it will very confusing and twisted story.But I think will be interested. That why the darkside stories never been told and release. Only stop at this figure only.