In my opinion these "secret mobs" are just little things added my mojang to make the game look cooler. But, what is going to happen 2 months from now? Explosive chickens? As random as this game already is I think that mojang should stop with the random mobs. Not that these mobs aren't fun but the game is getting very...scatter-brained
That . . . what. Spider Jockeys have been out for a year, charged creepers since the weather update, Giants were in Alpha and removed . . . the only new 'secret mob' is the cave spider, going by the theme you presented.
But even cave spiders aren't really secret ._.
I . . . don't really know how you managed to think Giants were new though XD
Spider Jockeries have been here since Alpha and they are not new nor is Radioactive Creeper aka Charged Creepers which has been here since Beta 1.5 and Giants were supposed to be here,but got was never added.
I believe after the halloween update when a spider spawns it has a 1/100 chance of being a spider jockey, although they seem to be more common since 1.8. Charged creepers were added in Beta 1.5 with weather. Giants have been around since survival test, and even spawned naturally at the time, but were removed in a later survival test version, leaving their code leftover. Now they don't spawn naturally or from a spawner, but can be hacked in through mods.
TL;DR(I think, I have no idea if that's the correct phrase or not: The former 2 can occur naturally but rarely, and the last one is just a test of a bigger zombie model left in from early survival test versions.
Private Mod Note
Rollback Post to RevisionRollBack
Users lack the mental capacity to have intelligent discussion, and mods lack the mental capacity to make intellegent decisions... I give up trying to share my intelligence with the world.