Filter land

Filter lands can refer to two different sets of dual lands. Their name describes the ability to take one mana and turn it into a combination of two colored mana. Some lower powered and older filter lands can generate more color but don't generate net mana, making them generally poor but lower rarity mana fixers.
==Original filter lands==
===Allied colored from Odyssey===
The original filter lands were a cycle of lands that appeared in Odyssey. They each have an activation cost of and produce two mana of different colors of an allied color pair. While better than some filter lands due to being mana-positive, the inability to tap for mana meant that they could leave a player stranded without mana.
*<c>Skycloud Expanse</c> 
*<c>Darkwater Catacombs</c> 
*<c>Shadowblood Ridge</c> 
*<c>Mossfire Valley</c> 
*<c>Sungrass Prairie</c> 
===Enemy colored from Fallout===
Twenty-three years after the introduction of the original filter lands, the cycle was completed with the printing of the remaining five enemy color filter lands in Universes Beyond Fallout. They immediately were reused in Universes Within Thunder Junction Commander.
* 
* 
* 
* 
* 
==Shadowmoor/Eventide filter lands==
Newer filter lands were previewed in Future Sight. The cycle of ten dual lands was finished in the sets Shadowmoor and Eventide. In Shadowmoor the cycle of allied-colored lands was printed, while Eventide had the cycle of enemy-colored lands. They each take one mana of two possible colors and produce two mana of any combination of the two colors that can be paid. They can also tap for mana, avoiding the above issue.
They were reprinted in Oath of the Gatewatch: Zendikar Expeditions and Double Masters
*Future Sight Timeshifted Shadowmoor preview
**<c>Graven Cairns</c> 
===Allied colored from Shadowmoor===
*<c>Mystic Gate</c> 
*<c>Sunken Ruins</c> 
*<c>Graven Cairns</c> 
*<c>Fire-Lit Thicket</c> 
*<c>Wooded Bastion</c> 
===Enemy colored from Eventide===
*<c>Fetid Heath</c> 
*<c>Cascade Bluffs</c> 
*<c>Twilight Mire</c> 
*<c>Rugged Prairie</c> 
*<c>Flooded Grove</c> 
==Ravnica Signets==
During Ravnica block a cycle of ten Mana Stones were printed which have abilities similar to the original filter lands. These artifacts cost to cast and can be tapped to filter into two mana of two different colors.
===Allied colored===
*<c>Azorius Signet</c> ()
*<c>Dimir Signet</c> ()
*<c>Rakdos Signet</c> ()
*<c>Gruul Signet</c> ()
*<c>Selesnya Signet</c> ()
===Enemy colored===
*<c>Orzhov Signet</c> ()
*<c>Izzet Signet</c> ()
*<c>Golgari Signet</c> ()
*<c>Boros Signet</c> ()
*<c>Simic Signet</c> ()
==Original triple lands==
The earliest triple land cycle from Homelands which produces three colors of mana conditionally as follows:
:: Add . 
:,: Add M. 
:,: Add N or O.
where N and O are the allied colors of M.
*<c>Aysen Abbey</c> ()
*<c>Wizards' School</c> ()
*<c>Castle Sengir</c> ()
*<c>Koskun Keep</c> ()
*<c>An-Havva Township</c> ()
By a looser definition, much like some of the lands listed below, these too are filter lands but are strictly worse than several of them.
==Rainbow filter lands==
Introduced in Lorwyn, <c>Shimmering Grotto</c> has the ability ", : Add one mana of any color." alongside tapping for , making them strictly better than older filter lands <c>School of the Unseen</c> and <c>Henge of Ramos</c>. This pair of abilities is the most common filter land template, and with reprints (plus <c>Unknown Shores</c>, which has one more premier set printing) turn up often in sets as a bad mana fixer where <c>Evolving Wilds</c> is potentially too useful, or players see multiple off-color costs for single-color cards. Newer common versions experiment with other minor upsides.
The following lands follow this template, with the rare ones having a powerful secondary ability.
===Common===
*<c>Cave of Temptation</c> from Modern Horizons Sacrifices to add two +1/+1 counters for .
**<c>Captivating Cave</c> from The Lost Caverns of Ixalan The same, but is a Cave.
*<c>Conduit Pylons</c> from Outlaws of Thunder Junction Surveils 1 when it enters, is a Desert
*<c>Crystal Grotto</c> from Dominaria United Scries 1 when it enters.
*<c>Heap Gate</c> from Commander Legends: Battle for Baldur's Gate Is a Gate, can also create Treasure.
*<c>Painted Bluffs</c> from Amonkhet Is a Desert.
*<c>Hidden Grotto</c> from Bloomburrow Surveils 1 when it enters.
*<c>Shimmering Grotto</c> from Lorwyn
*<c>Study Hall</c> from Commander 2021 Scries if used to cast their Commander.
*<c>Unknown Shores</c> from Theros
===Rare===
*<c>Abstergo Entertainment</c> from Assassin's Creed Returns a historic permanent from a graveyard to hand at the cost of and exiling itself and all graveyards.
*<c>Hall of Oracles</c> from Strixhaven: School of Mages Tap to add a +1/+1 counter to a creature, after casting an instant or sorcery.
*<c>Hall of Tagsin</c> from The Brothers' War Creates powerstones for .
*<c>Guildmages' Forum</c> from Guilds of Ravnica Puts +1/+1 counters on multicolor creatures cast with filtered mana.
*<c>The Mycosynth Gardens</c> from Phyrexia: All Will Be One Can turn itself into an artifact controlled by the land’s controller
*<c>Planar Nexus</c> from MH3 Commander Is all nonbasic land types
*<c>Talon Gates of Madara</c> from MH3 Commander Is a gate that phases out a creature on entry and can put itself onto the battlefield from the hand for .
==Other filter lands==
There are a few other filter lands that don't belong in any cycle:
*<c>Baldur's Gate</c> from Commander Legends: Battle for Baldur's Gate Adds mana of a chosen color for each of your other Gates for .
*<c>Cabal Coffers</c> from Torment Adds for each Swamp you control for .
*<c>Cabal Stronghold</c> from Dominaria Adds for each basic Swamp you control for .
*<c>Cascading Cataracts</c> from Amonkhet Adds five mana in any combination of colors for .
*<c>Castle Garenbrig</c> is an unusual case, as it belongs to a cycle in Throne of Eldraine, but the others do different effects. It filters into six for creature abilities or spells.
*<c>Crypt of the Eternals</c> from Hour of Devastation Adds , , or for .
*<c>Crystal Quarry</c> from Odyssey Adds for .
*<c>Great Hall of the Citadel</c> Adds two mana of any color for only to cast legendary spells.
*<c>Henge of Ramos</c> from Mercadian Masques Adds one mana of any color for .
*<c>Interplanar Beacon</c> from War of the Spark Adds two mana of different colors for , but to cast only planeswalkers.
*<c>Nykthos, Shrine to Nyx</c> from Theros Adds an amount of mana of a chosen color equal to your devotion to that color for .
*<c>Opal Palace</c> from Commander 2013 Adds one mana of any color in your Commander's color identity for .
*<c>School of the Unseen</c> from Alliances Adds one mana of any color for .
*<c>Tarnation Vista</c> from The Big Score Adds one of the appropriate mana for each monocolored permanent for .
*<c>Three Tree City</c> from Bloomburrow Adds an amount of mana of a chosen color equal to your creatures of a chosen type for .
==References==