I named a Shroomish “Sh-Boom” after the famous song by the do-wop singing group The Chords: “Sh-Boom Sh-Boom (Life Could Be A Dream”). Enjoy.
Shroomish might make a good cap!
Perhaps the name “Psilocybin” would work, but I generally do not like drug references.
Breloom (in Japanese: キノガッサ “Kinogassa”) is a dual-type GRASS-FIGHTING Pokémon.
I think that a good nickname for Breloom would be “Boom Boom” or “Mancini” after the former Lightweight boxing champion Ray “Boom Boom” Mancini.
Breloom is a FIGHTING type, and it looks like a boxer. Youngstown native “Boom Boom” Mancini is a notable part of boxing history. Mancini defended his title against Korean challenger Duk Koo Kim. Boom Boom easily defeated Kim, but knocked him around for 14 rounds. (Video linked here.) Kim suffered brain injuries that lead to his death four days later. Tragically, Kim’s mother then killed herself. Oddly, even the Caesars Palace referee for the bout Richard Green, also killed himself. These events haunted the very likable Ray Mancini, and the young boxer retired from the sport just two years later – but I digress once again …
For a female Breloom, I might suggest the name “Bloomers” as in a lady’s unmentionables.
If you have another name for these Pokémon, please leave your suggested names in the comments below!