If youve played a voltron deck before, youve probably experienced the pain of having your commander removed in response to an Aura or Equipment that protects them
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of Saheeli's second ability)
Some examples include equipment, which you can equip to creature cards to give them new abilities or make them more powerful
I often feel that custom designers are too inclined to make cards with too many abilities, or too complicated
Honorable Mentions The One Ring, Teferi's Protection, Perch Protection, Noble Heritage, The Stasis Coffin, and Absolute Virtue are all cards capable of giving you protection from everything which still stops spells and abilities from targeting you