Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a creature may become lethal if Oko's second ability changes its toughness during that turn
I find I often play it instead of something like a Time Spiral or perhaps even a Fact or Fiction as it will be pretty effective as a card draw mechanism but then also doubles up as an extra threat
As an artifact creature, it fits right at home in delirium decks as a payoff and a card that gets you halfway there once it hits the yard
For example, if one player has 10 life and the other has 17 life, the first player gains 7 life and the other one loses 7 life
Vito, Thorn of the Dusk Rose A classic groan-worthy black commander who is half the Exquisite Blood combo in the command zone, Vito, Thorn of the Dusk Rose is a fine deck, and better now with more support like Enduring Tenacity