Rule 702.42a

Entwine is a static ability of modal spells (see rule 700.2) that functions while the spell is on the stack. “Entwine [cost]” means “You may choose all modes of this spell instead of just the number specified. If you do, you pay an additional [cost].” Using the entwine ability follows the rules for choosing modes and paying additional costs in rules 601.2b and 601.2f–h.