That is a nice, simple answer, but it doesn't establish what "fourth-party" actually means. First, second, third, and fourth party are always defined with respect to a particular property owner, like, say, Nintendo. Speaking in terms of Nintendo...
- First-party franchises are franchises directly owned by Nintendo itself, such as Mario, The Legend of Zelda, and Splatoon. Nintendo has free reign to use these however it sees fit.
- Second-party franchises are franchises that Nintendo does not own directly, but does have partial ownership of; they are either owned by direct subsidiaries of Nintendo or Nintendo has co-ownership of them in a fashion where no extensive negotiations are needed for their use (unlike, say, Geno, who Nintendo has partial ownership of, but would still need to go through extensive negotiations with Square Enix to actually use (and Square Enix would likewise need to negotiate with Nintendo to use Geno... if you think this sounds like a headache for both parties, you'd be correct)). Examples include Pokémon (owned by Game Freak/The Pokémon Company International), Golden Sun (owned by Camelot), and Kirby (owned by HAL Laboratories). Though, funnily enough, Game Freak and Camelot aren’t entirely full subsidiaries of Nintendo, as they both have some franchises which they share ownership of with Sega instead (like Pulseman for Game Freak and Shining Force for Camelot). Basically, the difference between second-party and third-party is whether or not the parent company can be considered to be part of Nintendo. Nintendo can use second-party franchises pretty much whenever it likes, but does have to follow some guidelines in how it does so (the Pokémon Company, for instance, can be fairly tight-wadded in regards to how Pokémon is handled, and Nintendo could actually get in trouble if it were to "mishandle" the property). Also, Rareware franchises were considered second-party to Nintendo before the Microsoft buyout; they are now second-party to Microsoft and third-party to Nintendo.
- Third-party franchises are franchises that Nintendo does not own at all; they are owned by independent companies in the video game industry, and a third-party franchise having representation on Nintendo property requires some sort of agreement to be made between Nintendo and the franchise's parent company. Third-party franchises include Sonic the Hedgehog (owned by Sega), Mega Man (owned by Capcom), Castlevania (owned by Konami), and Final Fantasy (owned by Square Enix); Sony and Microsoft franchises such as God of War, Little Big Planet, Halo, and Banjo-Kazooie are also third-party for Nintendo, but given that they have their own first-party or second-party systems to be featured on, they aren't likely to be seen on Nintendo systems anytime soon. Kingdom Hearts is technically third-party as well, despite being owned by Disney (not Square Enix as a lot seem to think), as while Disney is not primarily a video game company, Kingdom Hearts itself is primarily a video game franchise. Indie franchises, such as Shantae (WayForward), Shovel Knight (Yacht Club Games), and Cave Story (Nicalis), are also third-party to Nintendo.
- Fourth-party franchises are not owned by Nintendo and are not primarily video game properties; they may have tie-in video game products, but video games will never be the primary focus of fourth-party franchises. Since Smash is meant to be about video games first and foremost, with a focus on Nintendo, fourth-party franchises really have no business with it. Fourth-party franchises include Dragon Ball (Toei), Shrek (Dreamworks), SpongeBob (Nickelodeon), and the Disney Animated Canon (take a wild guess).
Whether a character is first-party, second-party, third-party, or fourth-party is determined by the ownership of the franchise the character is from. The
Smash roster is primarily composed of first- and second-party characters, with a handful of third-party guests, but Sakurai has made it quite clear that fourth-party characters should not bother applying; they will
never be invited.
Tap-Tap was an ordinary enemy as well. Granted, it was an enemy that Yoshi normally could not hurt in any way (his tongue just pushed it a bit, his eggs just knocked it backwards, and stomping on Tap-Tap just hurt Yoshi); he had to use other things (like other Tap-Taps, Chomp Rocks, or Super Stars) to take a Tap-Tap down, and if no suitable objects were available... well, Yoshi couldn't do squat. Crazee Dayzees, by contrast, are very easily killed. So... yeah. Tap-Tap being weaker than Crazee Dayzee still doesn’t make sense.