Cost increasers/decreasers

[MedeaMelana]

Certain cards allow other cards to be cast without paying their mana costs (Mindclaw Shaman, Spelltwince, Omniscience). Paying mana costs for casting spells should therefore probably be done by the engine rather than actively by the cards themselves so that sometimes the engine can decide not to ask the player to actually pay these mana costs. Additional costs still need to be paid, however, including additional mana costs.

Furthermore, certain cards increase or decrease the total cost of a spell (its mana cost + additional costs).