Well it doesn't have any terrain requirements.
Code:
<!-- Mangrove -->
<FeatureInfo>
<Type>FEATURE_MANGROVE</Type>
<Description>TXT_KEY_FEATURE_MANGROVE</Description>
<Civilopedia>TXT_KEY_FEATURE_MANGROVE_PEDIA</Civilopedia>
<ArtDefineTag>ART_DEF_FEATURE_MANGROVE</ArtDefineTag>
<iMovement>2</iMovement>
<iSeeThrough>1</iSeeThrough>
<iDefense>25</iDefense>
<iPopDestroys>6</iPopDestroys>
<bNoCity>1</bNoCity>
<FootstepSounds>
<FootstepSound>
<FootstepAudioType>FOOTSTEP_AUDIO_HUMAN</FootstepAudioType>
<FootstepAudioScript>AS3D_UN_FOOT_UNIT_MUD</FootstepAudioScript>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>FOOTSTEP_AUDIO_HUMAN_LOW</FootstepAudioType>
<FootstepAudioScript>AS3D_UN_FOOT_UNIT_LOW_MUD</FootstepAudioScript>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>FOOTSTEP_AUDIO_ANIMAL</FootstepAudioType>
<FootstepAudioScript>AS3D_UN_ANIMAL_FOOT_LARGE_MUD</FootstepAudioScript>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>FOOTSTEP_AUDIO_ANIMAL_LOW</FootstepAudioType>
<FootstepAudioScript>AS3D_UN_ANIMAL_FOOT_LARGE_LOW_MUD</FootstepAudioScript>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>FOOTSTEP_AUDIO_HORSE</FootstepAudioType>
<FootstepAudioScript/>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>LOOPSTEP_WHEELS</FootstepAudioType>
<FootstepAudioScript/>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>ENDSTEP_WHEELS</FootstepAudioType>
<FootstepAudioScript/>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>LOOPSTEP_WHEELS_2</FootstepAudioType>
<FootstepAudioScript/>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>ENDSTEP_WHEELS_2</FootstepAudioType>
<FootstepAudioScript/>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>LOOPSTEP_TANK</FootstepAudioType>
<FootstepAudioScript/>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>ENDSTEP_TANK</FootstepAudioType>
<FootstepAudioScript/>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>LOOPSTEP_MOD_ARMOUR</FootstepAudioType>
<FootstepAudioScript/>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>ENDSTEP_MOD_ARMOUR</FootstepAudioType>
<FootstepAudioScript/>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>LOOPSTEP_ARTILLERY</FootstepAudioType>
<FootstepAudioScript/>
</FootstepSound>
<FootstepSound>
<FootstepAudioType>ENDSTEP_ARTILLERY</FootstepAudioType>
<FootstepAudioScript/>
</FootstepSound>
</FootstepSounds>
<WorldSoundscapeAudioScript>ASSS_OASIS_SELECT_AMB</WorldSoundscapeAudioScript>
<PropertyManipulators>
<PropertySource>
<PropertySourceType>PROPERTYSOURCE_CONSTANT</PropertySourceType>
<PropertyType>PROPERTY_AIR_POLLUTION</PropertyType>
<GameObjectType>GAMEOBJECT_PLOT</GameObjectType>
<RelationType>RELATION_NEAR</RelationType>
<iDistance>1</iDistance>
<iAmountPerTurn>-4</iAmountPerTurn>
</PropertySource>
<PropertySource>
<PropertySourceType>PROPERTYSOURCE_CONSTANT</PropertySourceType>
<PropertyType>PROPERTY_WATER_POLLUTION</PropertyType>
<GameObjectType>GAMEOBJECT_PLOT</GameObjectType>
<RelationType>RELATION_NEAR</RelationType>
<iDistance>1</iDistance>
<iAmountPerTurn>-5</iAmountPerTurn>
</PropertySource>
</PropertyManipulators>
</FeatureInfo>
If oasis can't be at river or coast and flood plain must be at river, then it should be doable for coast.
On what terrains it should be spawned?