Fog

Fog is a slang term used by Magic R&D to describe spells that prevent all combat damage that would be dealt in a certain turn. This mechanic is named after the Alpha card Fog and is primary in green and tertiary in white.

Fog, the exact rules text, has been done in white (Angelsong), black (Darkness) and green (Clinging Mists, Defend the Hearth) and fog variants have been done in blue (e.g. Hydrolash) and red (e.g. Feint). The multicolored Angus Mackenzie also has this effect. It started in green, spent numerous years bouncing around, ended up in white, and then finally got moved back to green where it has stayed.

Blue does it by granting -N/-0 to all of the opponent’s creatures (e.g. Lethargy Trap</c>).