finished fldeff_poison

src/bg.c

@@ -865,7 +865,7 @@ void SetBgAffine(u8 bg, u32 srcCenterX, u32 srcCenterY, s16 dispCenterX, s16 dis
     SetBgAffineInternal(bg, srcCenterX, srcCenterY, dispCenterX, dispCenterY, scaleX, scaleY, rotationAngle);
 }
 
-u8 Unused_AdjustBgMosaic(u8 a1, u8 a2)
+u8 AdjustBgMosaic(u8 a1, u8 a2)
 {
     u16 result;
     s16 test1;

src/fldeff_poison.c

@@ -0,0 +1,39 @@
+#include "global.h"
+#include "task.h"
+#include "bg.h"
+#include "sound.h"
+#include "constants/songs.h"
+
+static void Task_FieldPoisonEffect(u8 taskId)
+{
+    s16 *data = gTasks[taskId].data;
+
+    switch (data[0])
+    {
+    case 0:
+        data[1] += 1;
+        if (data[1] > 4)
+            data[0]++;
+        break;
+    case 1:
+        data[1] -= 1;
+        if (data[1] == 0)
+            data[0]++;
+        break;
+    case 2:
+        DestroyTask(taskId);
+        return;
+    }
+    AdjustBgMosaic((u8)(((u8)data[1] << 4) | (u8)data[1]), 0);
+}
+
+void FldEffPoison_Start(void)
+{
+    PlaySE(SE_DAUGI);
+    CreateTask(Task_FieldPoisonEffect, 80);
+}
+
+bool32 FldEffPoison_IsActive(void)
+{
+    return FuncIsActiveTask(Task_FieldPoisonEffect);
+}