Shadowverse

Cronos seems to drop for everyone, even for Revant.

It didn't drop for me. Although before, on the contrary, the legendary units used to drop regularly.

I heard that he is used in the portal, either instead of the Machine God, or together with it.

I saw a couple of such decks at the beginning of the expansion. It's probably cool to burn cards with heavy decks, but more aggressive decks will only be grateful for Cronos (although they will probably kill him before he comes into play).
There was also a P/D/K deck with him, but they disappeared somewhere after the nerfs.