Spiny

Spiny's are creatures in the Mario series. They first appeared in the NES classic Super Mario Bros., where Lakitus (whom have an unlimited supply of them) would aim and throw them from above toward Mario or Luigi (depending on who the player was). If he failed to do so, the Spiny would come out of his shell and try to harm one of the characters. You can not jump ontop of these creatures, because as the name suggests, they have spikes ontop of there shell. The only way to beat these pesky monsters is by using a fire flower or a starman. Also, if you can reach Lakitu, kill him before he has a chance to throw the spiny eggs.

Mario Bros.
In all of the rereleases of the arcade classic Mario Bros., Spinies have replaced Shellcreepers as enemies, though overall they perform the same manourvers.

The undefeatable Spinies
In the Nintendo 64 video game Super Mario 64, Spines would (very rarely) appear on Tiny-Huge Island and Rainbow Ride. In these stages, they would, like before, be thrown by Lakitus, however, this time there would be no way to defeat Spiny at all. This was the only game where you could not defeat a Spiny.

Appearance
Their appearance actually hasn't changed much over the years. They seem to look the same as they did over 20 years ago, while most other enemies' (most notably Koopa Troopas and Bowser) appearances has changed dramatically.