Why not put some Dragonball into the Watership Down universe?
Connoisseurs know, that in Dragonball, the characters can fuse into a new character. The name, that stands in the beginning is the leading part of the fusion (Hawig = Hazel leads, Bigzel = Bigwig leads). Only characters with a similar physique can fuse (so Bigwig and Pipkin would be impossible, e.g.). Because in DBZ, you have no mixed sexual fusions, I limited myself to same-gender-fusions (maybe except from the Watership Down kittens).
Watership Down:Bigwig + Hazel = Hawig or Bigzel
Hawkbit + Dandelion = Hawkdelion or Dankbit
Fiver + Pipkin = Fivkin or Piper (

)
Holly + Broom = Brolly (hey, we have a Dragonball character)
Primrose + Blackberry = Blackrose or Primberry
Snowdrop + Mallow = Malldrop or Snowow
Snowdrop + Gilia = Snowia or Gildrop
Gilia + Mallow = Mallia or Gillow
Strawberry + Blackavar = Blackberry (

) or Strawavar
Efrafa:Gorse + Thistle = Gorsle or Thise
Campion + Moss = Cammoss or Mosspion
Campion + Vervain = Verpion or Camvain
Red + Campion = Redpion or Camred
Red + Vervain = Redvain or Verred
Woundwort + Aspen = Aswort or Woundpen
Woundwort + Granite = Woundnite or Grandwort (I know, that Granite is not from Efrafa)
Redstone:Flax + Hickory = Flaxory
Gentian + Flax = Gex or Flantian
Hickory + Gentian = Hicktian or Genckory
Darkhaven:Shale + Feldspar = Shaldspar or Felle
Granite + Shale = Shanite or Grale
Other Fusions:Bluesky + Raincloud = Bluecloud or Rainsky