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.”

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.

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

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.

Doc Aurlock’s abilities can’t reduce the amount of colored mana you pay for a spell or ability. It reduces only the generic mana component of that spell or ability’s cost.

Doc Aurlock’s abilities don’t change the mana cost or mana value of any spell. They change only the total cost you pay to cast spells or plot cards from the appropriate zones.