I recommend a mix of specific, general, and vague terms. That assortment will cover the types of searches people are doing:
-Searches for a particular character or things from a specific piece of media.
-Searches for a general theme (i.e. "witches," "robots," etc.) that don't need to be from anything in particular.
-Searches for a vague vibe ("cute," "retro," "scary," etc.)
Best to be accurate, though. You'll get clicks if you mislabel something with popular terms, but that attracts bad attention, not good. Also, usually you don't have to use repetitive tags like "marx, kirby, kirby_marx." The only time I use repetitive tags is if it could be one or two words when people search for it (like pico_day and picoday).