You have not cast a creature spell using Muldrotha this turn.
({4} magic symbol) ({G} magic symbol) each turn available.
Steps
Activate three Islands by tapping them, adding ({U} magic symbol) ({U} magic symbol) ({U} magic symbol) .
Cast Walk the Aeons with buyback by paying ({4} magic symbol) ({U} magic symbol) ({U} magic symbol) and sacrificing three Islands, causing you to take an extra turn after this one and return Walk the Aeons to your hand.
Activate Ashnod's Altar by sacrificing World Shaper, adding ({C} magic symbol) ({C} magic symbol) .
World Shaper dies, triggering its second ability, returning all land cards from your graveyard to the battlefield tapped.
Cast World Shaper from your graveyard by paying ({3} magic symbol) ({G} magic symbol) .
World Shaper enters the battlefield, triggering its first ability, allowing you to mill three cards.