Timeless lotus and clay revanent
Play timeless lotus and try to cast clay revanent for mana using 1 green forest and 3 plains and using the rest of the mana by tapping timeless lotus. The goal would be to have black, red, green mana left over to spend on something afterwards.
You can't select how to spend that colored mana from timeless lotus and clay revanent comes into play with no counters on it and only half the counters it should on other creatures leaving red green and white mana still in your pool because you have a green white spell you could still cast in your hand.
Please make it easier to spend mana like this after being given a mixed handful of mana and needing finer control over how it is spent (maybe include it under "full control")