Rain D. is a large, fast-moving enemy unit that is encountered a few times in the Stories of Legend. At 100% strength magnification, its headbutt attacks deal ~5,000 damage each.
It is an annoying enemy due to the ridiculous number of knockbacks it can take, thus making units with a long attack animation ineffective (Bahamut, Super Galaxy Cosmo, etc.). Due to its decent range and attack damage, it can become a huge problem when multiple Rain D.s are stacked near your base, especially if they are buffed. Rain D.'s biggest weakness is fast-attacking ranged attackers (e.g Paris Cat, King Dragon, Ururun Cat).
Gets really depressed when Christmas comes around. Also hates Red. Don't ask why. Give the poor guy a break.
When Christmas comes, it really gets depressed. I also dislike red. Please do not ask the reason. Give a break to the poor.
Use Valkyrie or Delinquent Cat if you don't feel like saving up money for stronger cats (Dragon, Macho Legs, etc.). Spam Macho and Wall Cat to keep the reindeer distracted while your strongest cats do all the work. Bahamut is only effective when there is no other damaging unit you are using because of the knockbacks Rain D. takes.
Kill it fast by using cats that land huge amounts of damage per hit as it gets knocked back less times.