As of posting there are currently 188 images with Invalid Tag, which seems problematically high, and looking at the list of things aliased to it, possibly some of those should be aliased to something else, and others I question why they are on the list in general.
Aliases: furry, lucky bastard, furryfandom, community related, anal play, kill it, manebooru exclusive, bodily fluids, non-pony oc, derpibooru import, non-mlp oc, op is trying to start shit, not pony related, not cute, op is a duck, furry and pony, adorapipp, furryartist, furryyiff, furryporn, furryart, bhfyp, myart, furry girl, derpibooru exclusive, genital fluids, anthro art
Clearly the x exclusives are invalid (and any MLP image board default tags), but why are community/fandom invalid tags?
Most of the Fluids tags seem like they should instead be aliased to something (not sure what is the right tag), rather than invalid, and probably Anal Play as well.
And then the furry ____ seem again great targets for aliasing. Furry Art might be a bit vague, but “furry Porn” and friends could just default to “explicit”, “furry girl” is just “anthro” + “female”, “furry and pony” is “anthro” + “feral”.
Setting up more aliases would just cut down a lot on the need to do periodic invalid tag cleanups, and the current lis is so all over the place it’s near impossible to tell WHY something is getting marked invalid.