A new deleted scene has been released from Batman v Superman: Dawn of Justice and yes Consider this a spoiler warning for the film:
So we can assume that this is how lex gets arrested and ends up knowing what and who Darksied is. The same material that the strange creature is reminds me of the same material that Jor El shows Superman the rise and fall of krypton, so who is his mysterious creature? Well there’s no confirmation on who he his but he does have a slight resemblance to Steppenwolf, Darksied’s uncle.
Source: Collider