Oko, the Trickster

If the target creature is an illegal target by the time Oko's second ability tries to resolve, the ability won't resolve. Damage that would be dealt to Oko won't be prevented.

If Oko becomes a creature the same turn he enters the battlefield, you can't attack with him or use any of his {T} abilities (if he gains any).

Oko copies the printed values of the target creature. It won't copy counters on that creature or effects that have changed its power, toughness, types, color, or so on. Notably, it won't copy effects that made the target creature become a creature if it isn't normally a creature.