Zombie Rainbow has a great health stat for its price with the crippling delay as a major downside. Similar to Damaged MOAB, it can be in decks looking for high value Bloon cards that don't care about this delay.
The undead status paired with this high health per cost ratio from revive makes it useful to defend Camo Bloons such as Camo Green Bloon, alongside other spammable undead Bloons such as from Undead Army and Necromancer.
Zombie Rainbow Bloon had its Health increased from 200 to 220 in the Version 6.2 playtests. Initially, it was considered overpowered before the Revive nerf added prior to the public release of Version 6.0, but more balanced after that nerf.[1] Zombie Bloons were deemed to be underpowered in general, so a community playtester proposed the aforementioned buff,[1] which was accepted for the update by Ninja Kiwi.