Wow very nice, may I ask what are the Coordinates for the Guardian Grinder?
Also I didn't know one could make a creeper grinder, I thought they just had to be farmed in a generic mob grinder that also farms other mobs as well (since creepers spawn naturally along with other mobs.
It's a bit of that, yes. There are some height and block adjustments you can make so only creepers can spawn in it. Also, they are afraid of cats, so they'll walk off the edge to get away from them. I THINK something has changed in MC though, because this one stopped working. I tried a couple other variations, and it has not improved. I have to dig into it a bit and get it working again. I just revamped the Wither Rose and it's working crazy right now.
Ah I see, that's unfortunate. Hopefully you'll be able to get it working in the future, sometimes changes can be a minor setback, others they can be devastating. I remember my friend made a slime farm in a Swamp (this was a long time ago) then they changed it so other mobs spawn in Swamps and Slimes only spawn in Swamps on the full moon, that change essentially rendered his farm useless. Hopefully this change won't be as major a setback.