.breff

A Binary Revolution Effect File (.breff) is a file that controls how graphical effects work in-game. BREFF files get their textures from a corresponding BREFT file, which holds the textures. In NSMBW, both the BREFF and the corresponding BREFT file all have the prefix  (Wii New Mario?), followed by the actual name of it. If you'd like to know more about the effect files in NSMBW, see this page.

Opening BREFF Files
You can open BREFF files in BrawlBox or BrawlCrate.

File Format
The Sub File Item explained here points to this structure.

Emitter
An emitter usually has size 0x14c.

Particle
Like the emitter, the particle structure has a UInt32 telling how large this section is.

Afterwards comes the particle data.

Between this and the next structure there might be some padding to make the next structure aligned.

Animation
It seems like the tables contain the actual animation data. The tables comes directly after this section and they appear in the order KeyTable, RangeTable, RandomTable, NameTable and InfoTable.

NameTable
This table seems to link to one or more sub file item.

After comes the sub file item name references. All entries comes after each other and after the last, there might be some padding to align the next structure.