The toymaker frowned in bewilderment. None of his creations had ever sneezed before.

Millikin

{T}, Mill a card: Add {C}. (To mill a card, put the top card of your library into your graveyard.)

"Another failure," grumbled the toymaker. She slammed the door with such gusto that she failed to notice the eyes watching her.

Dominaria Remastered

Modern Horizons 2

The List

Eternal Masters

{T}, Put the top card of your library into your graveyard: Add {C} to your mana pool.

Odyssey

oc
T, Put the top card of your library into your graveyard: Add one colorless mana to your mana pool.

If an effect allows you to look at the top card of your library any time or to play with the top card of your library revealed, and you activate Millikin’s mana ability while casting a spell, you can’t look at the new top card of your library until you are done casting the spell. The same is true if you activate Millikin’s ability while activating another ability.