It seems that even if you play it, the state is such that 'the opponent can perform an additional exhaustion.' It is already known, and there are players who are actively exploiting this bug when it is played, so I strongly recommend not using it while the bug persists
If the target creature is an illegal target by the time Oko's second ability tries to resolve, the ability won't resolve
While Saskia lacks any specific Human kindred synergies, its color access and aggressive nature make it a solid choice for the tribe
If a player has fewer cards remaining in their library than the number of rad counters they have when the triggered ability resolves, they'll mill as many cards as they can
Since card advantage and attrition are vital components of winning control decks and strategies, board wipes, or spells that remove all of a certain type of permanent from the battlefield (usually creatures) are great ways to break parity, remove a lot of opposing resources, and address a lot of potential threats at once