Added the elemental trait for the Dust Devil and the Fire Guardians.

data/campaigns/Under_the_Burning_Suns/units/monsters/Dust_Devil.cfg

@@ -3,6 +3,7 @@
     id=Dust Devil
     name= _ "Dust Devil"
     race=monster
+    {TRAIT_ELEMENTAL}
     usage=scout
     image="units/monsters/dust-devil.png"
     level=1
@@ -37,19 +38,6 @@
         cold=150
         arcane=140
     [/resistance]
-    # all dust devils get an invisible trait that sets the not_living status for
-    # them so that they are immune to poison and healing
-    [trait]
-        id=dustdevilimmunities
-        availability="musthave"
-        male_name=""
-        female_name=""
-        description=""	# wmllint: ignore
-        [effect]
-            apply_to=status
-            add=not_living
-        [/effect]
-    [/trait]
     [attack]
         name=twister
         description= _ "twister"

data/campaigns/Under_the_Burning_Suns/units/monsters/Lava_Monster.cfg

@@ -3,6 +3,7 @@
     id=Lava Monster
     name= _ "Fire Guardian"
     race=monster
+    {TRAIT_ELEMENTAL}
     image="units/monsters/fireghost.png"
     {DEFENSE_ANIM "units/monsters/fireghost-defend.png" "units/monsters/fireghost.png" groan.wav }
     hitpoints=20

data/campaigns/Under_the_Burning_Suns/utils/traits.cfg

@@ -0,0 +1,17 @@
+#textdomain wesnoth-utbs
+# Traits definitions
+
+#define TRAIT_ELEMENTAL
+    # Units with trait Elemental cannot be drained, poisoned or plagued.
+    [trait]
+        id=elemental
+        availability="musthave"
+        name= _ "elemental"
+        female_name= _ "female^elemental"
+        description= _ "Immune to drain, poison and plague"
+        [effect]
+            apply_to=status
+            add=not_living
+        [/effect]
+    [/trait]
+#enddef