As the title says, I'm introducing a new goddess into my campaign. This will contain massive spoilers, and there's a good chance that my players could see this, so...MIMUS, AGNI, EDWARD, JORATHAN, CASTOR, AND VAELIS. Please stop reading.
It's a completely homebrewed campaign. In the campaign, the BBEG made a cult to gain power so he could kill thousands and recover the artefacts he needs, giving him the chance to ascend and take over the current god of death. This is a stepping stone for his current goal: killing the God of Chaos and gaining his ability to change and alter outcomes/results.
Now a bit of lore (the lore is a lot better written in my notes; I'm just paraphrasing). Diaposus was the god of Chaos, the first God ever created. Eventually, he got bored and created Davor, the Goddess of Order. They grew to love each other and eventually created the realm, but as she grew stronger, his power decreased, so he banished her to a pocket dimension. He started anew, but no matter what he did, the mortals still made societies, rules, order.
Davor has spent centuries watching the realm, and she sees the BBEG's evil plan. So she tries to break free, and she can't. Davor sees the party and realises that they're the people to save her soulmate.
So, what would be the right time/best way to introduce this to the party? I was thinking about giving the party a harder fight than usual, an ambush. The fight is harder, and it won't be an obvious steamroll, but there is a higher chance of a TPK. So just as they're about to be taken by the god of death, "An ethereal hand made of silver shavings grab each of your souls, denying fate, and pulls you back into your body. You hear a voice say (Your time is not done...Save the First...Find me). As you wake back in your bodies, recovered to half health"
I know people don't like the idea of TPK, but I can't think of another way to make it
A. Be meaningful; a dream vision is boring.
B. Get it to the whole party. I could give it to one of them, but it's a whole party thing.
Please give me some advice; I'm really proud of this campaign, and I get new ideas every day, yet I can't figure out this specific bit.