Simple mode

Stacking effects

One effect gives you a look. Two give you something nobody else has. Effects layer, each running on the output of the one before it, and the whole stack stays adjustable at every level.

Adding a layer

Press Add effect in the Effects section and pick an engine. It lands at the bottom of the stack and immediately runs on whatever the layers above produced.

  Dome                      ← base mesh, untouched
   ├─ Rhea Density          ← subdivision to a workable face count
   ├─ Rhea Engine 1  Cells  ← honeycomb shell
   └─ Rhea Engine 2  Displace
                            ↑ displaces the shell, not the dome

That distinction is the whole idea. The second engine never sees your original dome — it sees the honeycomb the first engine made. Reverse the order and you get a displaced dome that is then turned into cells, which is a different object entirely.

Managing the stack

Move up / down: Reorders evaluation. Almost always worth trying both ways before deciding a combination does not work — the two orders rarely resemble each other.
Duplicate: Copies an entry with its settings. Useful for two passes of the same engine at different scales: coarse cells, then fine cells over them.
Remove: Deletes one layer. Everything below re-evaluates without it. Nothing else in the stack is disturbed.
Enable / disable: Turns a layer off without removing it, so you can see what it was contributing. This is the fastest way to diagnose a stack that has stopped making sense.

Disable before you delete

When a stack produces something unreadable, disable layers from the bottom up one at a time. The layer that changes the result when you disable it is the one doing the damage, and it is very often not the one you suspected.

Combinations that work

Eroded, then Cells. The displacement roughens the surface first, so the cells that follow inherit irregular sizes. Better than turning Randomness up on the cells alone, because the irregularity has structure to it.
Cells, then Displace. A honeycomb shell that bulges and sags. This is what makes a shell look grown rather than printed.
Ridged, then Tessellate. Copies follow the ridges, because they sit on the displaced surface and inherit its normals.
Lattice, then Lattice. Two strut networks at different thicknesses, one bracing the other. The second inherits the first's edges, so they interlock rather than intersecting randomly.
Cells, then Tessellate. Components placed on the faces of a honeycomb rather than on a smooth surface. Expensive, and spectacular.

Combinations that will disappoint you

Two heavy cellular effects. The second sees a mesh that is mostly holes, and struts on struts read as noise. Use one cellular layer and vary it with a field instead.
Tessellate under anything. A tessellated mesh has a very high face count and no coherent surface. Engines above it will be slow and the result will be unreadable. Put tessellation last.
Density inside a stack. Raising density with three engines above it multiplies through all of them. Set the density you want first, then build the stack.

Apply, revert, and what each one costs

Apply: Collapses the whole stack into plain mesh data. The controls disappear, the modifiers go away, and you have an ordinary Blender object. Irreversible except by undo, so save first if you might want the recipe back.
Revert: Removes every Rhea modifier and hands back your original mesh exactly as it was. Because nothing was ever destructive, this really is exact — not an undo of a change, but the removal of something that was always sitting on top.

When to apply

Before sculpting, retopologising, or doing anything that needs real geometry to grab hold of.
Before exporting to a game engine or a slicer, unless you are exporting a format that bakes modifiers anyway.
Before running the applied-kind modules — Conway, growth, reaction-diffusion, Voronoi, form finding — on the result. They read mesh data, not modifier output.
When the stack has become slow enough to interfere with working, and you have stopped adjusting it.

When not to

If you might still change your mind, do not. A live stack costs you some viewport performance and nothing else. Applied geometry costs you every decision that went into it.

Apply a copy

Shift+D duplicates the object with its whole live stack intact. Apply the duplicate, keep the original. This is the habit worth forming — it takes a second and it has saved a lot of afternoons.

A note on density

The Density control at the top of the Effects section is a Rhea-managed subdivision modifier that sits below the whole stack. It uses simple subdivision rather than Catmull-Clark, on purpose: you asked for more faces, not a different shape. Catmull-Clark would round your cube into a sphere and quietly destroy whatever you modelled.

Density is a target rather than an increment. Setting it on a mesh that is already denser than the target does nothing, which is the behaviour you want — otherwise applying an effect to a dense sculpt would push its cells below a pixel and the result would read as a solid blob.