[[quoteright:325:[[TabletopGame/MagicTheGathering http://static.tvtropes.org/pmwiki/pub/images/boab36_prisStrands_3248.jpg]]]]
[[caption-width-right:325:[[RussianReversal In Soviet Russia, land fights for you!]]]]

->''"You rise with the Moon, I rise with the Sun."''
-->-- '''Zuko''', ''WesternAnimation/AvatarTheLastAirbender'', "[[Recap/AvatarTheLastAirbenderTheSiegeOfTheNorthPart1 The Siege of the North, Part 1]]"

In RealLife combatants naturally seek the high ground and other places on the battlefield with tactically advantageous GeoEffects, and to [[DefensiveFeintTrap maneuver their opponents]] into tactically disadvantageous positions. A related tactic is to affect allied and enemy morale to make the fighting easier. In fiction the Field Power Effect is a third, supernatural way to make a given set of characters (whether heroes or villains) stronger or weaker.

A Field Power Effect is a spell or environmental condition that affects the fighting ability of one or more characters, strengthening and/or weakening them. [[WeatherOfWar Weather]] and terrain may play a factor, such as a [[PlayingWithFire pyrokinetic]] being weak during a rainstorm while an [[MakingASplash aquakinetic]] gains more power. Or a [[ThePowerOfTheSun solar powered]] hero being strongest at noon and weakest when in pitch black darkness. Terrain like the PlaceOfPower affect characters atuned to the type of energy it boosts (and it's opposite). You can probably tell that due to ElementalRockPaperScissors, any Field Power Effect that boosts one set of ElementalPowers will weaken whatever is in its opposition. This is similar to how opposing sides with the ability to use StatusBuff and StatusBuffDispel can also end up canceling each other out. Other possibilities include things like time of day, year, or even the positions of planets and stars.

The reason Field Power Effects work is they somehow affect the PowerSource of characters, or failing that their soul. An area filled with Light energy naturally strengthens characters who [[LightIsGood are good-aligned]], while evil characters who are WeakenedByTheLight [[GoodHurtsEvil will suffer]] a {{Depower}}ing. It'd take a ''very'' strong CrossMeltingAura on the part of a villain to overpower that kind of disadvantage. The reverse is also true, an evil wizard who emanates [[TheDarkSide Dark Side]] energy will make heroes quake and those AllergicToEvil outright faint. In both cases the character will [[ImHavingSoulPains feel soul pains]].

Just to clarify, it's also possible for a Field Power Effect to ''just'' boost or drain without pairing both.
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!!Examples:

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[[folder:Anime and Manga]]
* Happens in ''Anime/DigimonAdventure'', when Etemon uses his Dark Network to depower the main 'mons.
* Used in ''InuYasha,'' occasionally. From dusk to dawn, on the first night of the new moon, Inuyasha turns human, returning to full power at sunrise.
* During the Black Moon arc of ''SailorMoon'', she was subjected to a variable gravity field onboard the villain's ship. She managed to pull off HeroicResolve and save her friends, standing (despite his increasing the gravity on her) and attacking him.
* Some of the players in ''Manga/{{Saki}}'' are like that. Koromo draws strength from the night and the moon, so she's at her absolute strongest when the finals take place during a full-moon night. Yuuki is strongest during the East Wind, referring to herself as 'The Thunder of The East', while Nanpo Kazue is strongest during the South Wind. (A battle between Yuuki and Kazue has her hang on by a thread during the East Wind, and then make a huge comeback during the South Wind, winning the game by a large margin.) Initially, Nodoka also had a FieldPowerBonus when playing Online, losing significant power when playing in person, but she eventually gained the ability to go into full 'Online Mode' in a live game, though it usually takes her a while...
** The most {{egregious}} [[AssPull of them all]] however, is [[spoiler:Shizuno's. The deeper the other players go into the stack, the weaker their gimmicks are]]. This perfectly counters both Awai's and Saki's ability.
** Saki herself has several points to this as well, such as finishing with her signature ''Rinshan Kaihou'', literally meaning 'A Flower Blooms On a Ridge' (go check what the terms mean somewhere else), would show a flower field around her.
* ''Franchise/YuGiOh'' has several dozen spells that give and remove field power bonuses and penalties. In the Duelist Kingdom arc of the [[Manga/YuGiOh manga]], monsters get a 20% Field Power Bonus (actual name) to attack and defence in their preferred terrain - so bugs get it in forests, undead in wasteland, etc.
* In ''Manga/FullmetalAlchemist'', alchemy takes its power from geothermal energy. The BigBad, Father, can block this energy, rendering alchemy useless in a given area. It does not block the similar magic of alkahestry, however, which has a different power source.
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[[folder:Tabletop Games]]
* This is the point of Nexus cards in ''TabletopGame/BattleSpirits''
* ''DungeonsAndDragons''
** 1st and 2nd Edition had a number of spells that helped groups of characters.
*** Bless: Raises morale and "to hit" rolls by 1.
*** Chant/Prayer: All attacks, damage and saving throws are at 1.
** The 2nd Edition supplement ''Tome of Magic'' had several priest spells of the War sphere that improved the performance of military units.
*** Courage, Morale and Rally all improved a unit's morale.
*** Adaptation allowed the unit to fight as if they were in their favored terrain type.
*** Selective Passage cut the movement cost (to travel through an area) in half.
*** A spell called Consumptive Field that drains hit-points from all characters in a area, potentially lethally, transferring them to the caster.
* ''{{Exalted}}'' has several examples related to the Exalt type.
** To give a few examples: this is how the Yozis' [[NoSell perfect defenses]] work. Malfeas' can only be used in developed areas (ranging from primitive villages to the Capitol of Heaven), Ebon Dragon's can only be used where Creation's sun doesn't shine, while Kimberry's can only be used near big enough body of water.
* The spells "Hallow" and "Unhallow" from ''DungeonsAndDragons'' cause an area to favor good-aligned or evil-aligned characters respectively.
* ''MagicTheGathering'' has dozens of such spells for specific colors and creature types.
* ''[[TabletopGame/GeistTheSinEaters Geist]]'' has the Boneyard Manifestation. A Sin-Eater using it is aware of everything within the area encompassed and can perform subtle manipulations to impose penalties or inflict damage on entities inside it, depending on the Key used. They can also remotely use other Manifestations within the Boneyard. And at maximum level the Boneyard's radius is measured in ''miles''.
* The whole point of Field Spell Cards in TabletopGame/YuGiOh, at least in early metagames, is this. With newer cards, Field Spell Cards start to do less archetypical effects. In any case however, the fact that [=FSCs=] affect both players' field can mean that whatever its effects are, it can also be used by a smart opponent.
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[[folder:Video Games]]
* In the ''AgeOfWonders'' games, wizards can cast certain spells that affect an entire battlefield. Examples include Holy Light, which brightens the scenery and buffs Good units and debuffs Evil units, and it's Evil counterpart, Unholy Darkness, which does the opposite.
* In ''BattleForWesnoth,'' lawful units fight better at day, and chaotic units fight better at night (and both fight worse at the opposite daytime). As well, the Mage of Light unit can illuminate an area with their presence, being a FieldPowerBonus for lawful and a FieldPowerDrain for chaotic units at the same time.
* ''VideoGame/ChronoCross'' has a field effect that, when biased completely to one colour, empowers spells of the same element and weakens those of the opposite and makes SummonMagic of that element useable. Good luck doing this when enemies are using their own spells. One character has a special ability where he changes the field colors to all one color (he spills paint), but you can't choose the color. There are also normal spells that can change the field to a single color except black and white.
* One of ''VideoGame/ExitFate's'' Demon Commandos possesses a spell permanently buffing up his own party, and the other one has a spell {{Field Power Drain}}ing the enemy party.
* In ''VisualNovel/FateStayNight'', both Caster and Rider use such effects to absorb energy, although we only see the effects on the field created by Rider, when it drains life power from the students of the school. Also, Ryuudou temple seems to fulfill a similar role, weakening all the servants who enter it ([[InformedAbility or so we are told)]].
** [[RealityWarper Reality Marbles]] also do this, imposing the user's {{mental world}} on their surroundings.
* ''Franchise/{{Pokemon}}'' has Weather Effects that benefit specific types, moves and abilities. It can be on Routes starting from Gen. 3, or you can set it up with respective moves or abilities.
** Rain boosts [[MakingASplash Water moves]], weakens [[PlayingWithFire Fire moves]] and makes Thunder and Hurricane 100% accurate.
** Sun does the opposite to Fire and Water moves, makes Solarbeam skip charging and make Moonlight, Morning Sun and Synthesis heal more HP.
** Sand hurts all Pokemon that aren't [[DishingOutDirt Rock, Ground]], [[ExtraOreDinary or Steel-type]] (or have an ability to make them immune). It also gives Rock-types a well appreciated Special Defense boost.
** Hail hurts all Pokemon that aren't [[AnIcePerson Ice-type]] (or have an ability to make them immune) and makes Blizzard 100% accurate.
** Several abilities also have something to do with the above weather effects. They either [[LightningBruiser double their speed]], make them gain HP gradually, or power up their moves.
** There's also Fog which lowers Accuracy, but you can't activate it on your own.
** [[TheCorruption Shadow Sky]] causes gradual damage to all non-Shadow Pokemon. The reverse of Fog; it MUST be manually activated, as Shadow power is unnatural.
*** On a side note, Kyogre and Groudon have the ability to cause Rain and Sun, respectively, simply by being on the field until overwritten by another move. Rayquaza and Golduck [[AntiMagic nullifiy]] field effects simply by existing on the field.
**** Other Pokemon gained these abilities in gen V...Ninetales has the Drought ability and Politoed has Drizzle.
** In addition, the "Room" series of moves also operate like field effects. Trick Room, introduced in Gen IV, reverses the effect of speed on action order so that slower Pokemon act first. Gen V's Magic Room and Wonder Room respectively nullify the effects of held items and reverse all Pokemon's physical and special defense stats.
** ''VideoGame/PokemonXandY'' added Terrain moves, which are similar to (And can stack with) weather, but with the restriction that they only affect Pokemon standing on the ground.
*** Grassy Terrain regenerates the HP of Pokemon and powers up Grass type moves.
*** Electric Terrain prevents Pokemon from falling asleep and powers up Electric type moves.
*** Misty Terrain prevents Pokemon from getting status effects and weakens Dragon type moves.
* The weather in ''VideoGame/FinalFantasyXII'' had an effect on both magic and attacks: If conditions were right, [[FireIceLightning elemental magic]] was strengthened (e.g., fire magic being stronger on a sunny day), and in bad weather conditions (thunderstorms, snowstorms) the accuracy of ranged weapons suffered.
* In one of the last missions of ''VideoGame/{{Infamous 2}}'' a big thunderstorm appears over the city. The storm allows Cole to recharge his powers by drawing energy from the heavens themselves, making him virtually invincible.
* In the ''VideoGame/TouhouOmenTrilogy'' games, the Land Meter is this. It affects the power of elemental attacks, causes enemies and party members with regeneration in an element to regenerate HP, and can allow or forbid the use of certain spells.
* A core game play element in ''VideoGame/{{Archon}}''. Units fight best (and in particular have the most health) on squares matching their own side. Some squares are permanently light respectively dark, others cycle through several intermediate stages indicated by color. There is even a spell to reverse/invert specifically that cycle.
[[/folder]]

[[folder:Web Comics]]
* ''Webcomic/TheOrderOfTheStick'': The Azure City throne room is consecrated. Notably, it makes any attempt by an evil cleric at [[TurnUndead "turning"]] the Ghost-Martyrs of the Sapphire Guard more difficult. It takes one as powerful as Redcloak to have any chance of succeding.
[[/folder]]

[[folder:Western Animation]]
* In ''WesternAnimation/AvatarTheLastAirbender'', Firebenders and Waterbenders gain strength from the sun and the moon, respectively. Firebending is stronger during the day, and Waterbending is strongest on the night of a full moon.
** The sun and moon's respective eclipses render their associated bending art unusable. [[spoiler: It's used in the Siege of the North, and fuels the plot for about 1/3 of the series]].
** Fire Lord Sozin also decided to [[spoiler: make his ''own'' FieldPowerEffect with a "comet" that drastically powers up Firebending]]. He used it to [[spoiler: wipe out the Air Nomads, 'cept for the one they were looking for]], and 100 years later, his descendant, Ozai [[spoiler: tried to burn the whole ''Earth Kingdom'' at the comet's return]].
** The series' Bible also states Earthbenders gain power from fault lines, and Airbenders from higher altitudes. Neither is elaborated upon in-show. Other effects, like rain, are self explanatory ([[http://www.racebending.com/v3/wp-content/uploads/2009/10/ipbible.pdf here]]).
* ''{{BIONICLE}}'': the energy in Karda Nui causes beings of the [[LightEmUp Light]] ElementalPowers to grow larger.
* The Disney ''WesternAnimation/{{Gargoyles}}'' sleep during the day, and awake at sunset. A somewhat extreme example, since they're helpless from sunrise to sunset.
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