If you’re casting a plotted card from exile without paying its mana cost, you can’t choose to cast it for any other alternative costs. You can, however, pay additional costs, such as kicker costs. If the plotted card has any mandatory additional costs, those must still be paid to cast the spell.

When Beastbond Outcaster enters the battlefield, its triggered ability will check to see if you control a creature with power 4 or greater. If you don’t, the ability won’t trigger at all. If the ability does trigger, it will check again as it tries to resolve. If you no longer control a creature with power 4 or greater (usually because the applicable creature is no longer on the battlefield), the ability won’t do anything.

Plot abilities are written “Plot [cost],” which means “Any time you have priority during your main phase while the stack is empty, you may pay [cost] and exile this card from your hand. It becomes plotted.”

If a plotted card has in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

You can’t cast a plotted card on the same turn it became plotted. On any future turn, you may cast that card from exile without paying its mana cost during your main phase while the stack is empty.

Exiling a card using its plot ability is a special action. Once you announce you’re taking that action, no other player can respond by trying to remove that card from your hand.