Create Single rain droplet:
Create sphere → T → Subdivision Axis, Height: 8 (rename the layer as Rain)
Vertex mode → B (Soft selection) → Select upper vertex on sphere → move up the shape (extend the body), then scale the top head vertex (sharpen the head) like follow:
Poly modelling mode → Object mode → Freeze transformation → Delete by Type → CentrePpivot
→ Scale the raindrop down to all XYZ to 0.04
→ Freeze.... repeat the steps above except scaling
→ Translate Y: 8 (repositioning)
Create continuous animation:
Key Select (Shift+W) @ 0F, Translate Y: -8@ 80F
Window → Animation Editors → Graph Editor
Select all points and make as Linear
→
Curves (top bar in Graph Editor) → Post Infinity → Cycle with Offset (let the rain back to start position when timeline runs back to 1F)
Group the Rain layer (Ctrl+G), rename as Rain_GRP → Rotate X: 15
Select rain grop → MASH → Create Network → Grid Distribution Type → Distance XZ 15, GRID XZ 25
→ Add Random Node: Positon X: 0, Y:10
Make Rain fall randomly (non unified):
In MASH, Add Transform Node → R click on Control Null → Create (a layer called MASH1_Transform_Ioc created in Outliner)
→ Select the transform layer in Outliner → Translate Y: 10
→ In MASH, Add Time Node: Animation Start and End: 1, 120; Random Seed: 10, Time scale: 1.4, Random Time Scale 10
Go to FX (F5) → Fluid → Pond
Select both MASH1_ReproMesh and Pond layer in Outliner → Fluids → Make Collide
Select Pond layer → Attribute editor set as follows:
Boundary X and Y: None
Dynamic Simulation → Damp: 0.1
Contents Details → Density → Density Scale: 0.04
Select Pond → Modify (top bar) → Convert → Fluids to Polygons (pond layer auto rename as PolySurface)
Select both MASH ReproMesh and PolySruface layer, Cache → Alembic Cache → Export Selection to Alembic (start to end frame) → Export
Open New scene, import the Alembic → Group the ReproMesh and PolySurface, rename as Rain
→ Apply Standard surface material → Change Type to AI standard surface → Presets → Deep Water → Replace
Select the Rain Group → Edit → Duplicate special box → Geometry type: Copy, tick Duplicate input graph → Duplicate Special
Move the duplicated Rain1 layer align next to original layer, scale Rain1 layer to -1
→ Go to Alembic node in Rain1 → Offset: 4 (to make rain comes later than original surface)
Group original Rain and Rain1 layer, duplicate (Shift+D) and align next to each other, scale X to -1 of new layer
(animation in duplicated layer may not work, if so, use duplciate special as above instead)