The Ghostly Prison effect or Propaganda effect refers to a passive ability on cards that tax attacking creatures for mana. Once in blue, the effect is now primarily white, as a tax effect to prevent creatures attacking (two white abilities).
History
This effect started, oddly, in Black with Koskun Falls in Homelands. Winter's Chill has an effect that somewhat follows the idea behind the Prison effect, but it has too many odd conditions to truly count as one. The most iconic and elegant version was Propaganda in Tempest, following which two more were printed in Blue before shifting to White in Windborn Muse. It has been White since then - Ghostly Prison in Champions of Kamigawa was a colorshifted reprint of Propaganda, and hence has been the source of the mechanic's name since.
That said, it took until New Phyrexia for a new variant to be printed, and with it, a new template. Planeswalkers were released in the meantime as an important game piece, and effects of the like now tax attacks on planeswalkers of the effect's controller. The tax has also halved from 
to 
to prevent overly crippling opponents in longer games.
List of attack taxers
- Koskun Falls
- Elephant Grass
- Propaganda
- War Tax (activated ability)
- Collective Restraint
- Windborn Muse
- Ghostly Prison
- Norn's Annex (
cost) - Sphere of Safety
- Archangel of Tithes
- Baird, Steward of Argive
- Forbidding Spirit (single triggered ability)
- Archon of Absolution
- Nils, Discipline Enforcer