Graves somehow frees himself, tricks or straight up overpowers Grindelwald, and, in his rage, brutally rapes and murders him.

I also want to see Graves struggling to deal with the aftermath: part of him knows that what he did was monstrous and unforgivable, but the part that's been broken and corrupted thinks that not only was it justified considering what Grindelwald put him through, it actually felt immensely good...

The outcome is up to you.