WOW WOW you're really trucking.
Ultimate ABC was created after the original. To get ready for TWO basicly you need to be able to/learn how to animate. The Ultimate ABC leads you through different skill levels better, and if you go through it you have a demo reel to show you can animate. I think the TWO team is looking for that demo reel, so they can judge how well you can animate.
Check the pinned thread at the top of the students forum, I'm going to go in and add excercises for Ultimate ABC after I give you a critique.I'm impressed by how much work you've been doing!
So.
ABC 1B: The little yellow ball looks pretty good, you could add a small 2nd bounce in there. The bigger ball looks okay. The angle of the squash and stretch should be along the same angle of the trajectory, right now it's up and down. The diminishing bouncing is fair, but the arcs look off (not consistent), try turning on Onion Skin (from the Tools->Option window) or get a dry erase marker and follow it on your screen. The first stretch and squash look pretty good. Often the ball stretches as it's going upwards, which you haven't captured here on the bounces, try putting it in and see how it feels to you.. I see that you are doing a good job of getting that nuetral shape at the top when the energies are neutralized, and I see you are doing a good job of diminishing the squetch as the bounces get smaller.
Bouncing Ball:
It's hard to judge since it's in slow motion. Try getting it up to speed, because one of the reasons we do bouncing balls is to work on timing as well. The stretch as it falls is good, and good stretch coming back up stretchy then neutralizing out. The squash looks okay, but I'm not sure how strong it's going to look at normal speed. If you look at that picture I posted, it's an old animation trick to have the stretchiest pose right before it hits, then next frame is the most squashiest, then a couple of frames of transition back to stretchy on the way out, gives the impact more oomph.
ABC 1 CF: Very cute. Fun. I think you could sell the sad feeling of the larger ball if it didn't stick at full deflation, but more deflated but then breathed a little so we could see it's in a sad state emotionally and not just physically. You've got some cute personalities developing but I kind of want to see some more evidence of physics mastery (as in more hopping) also. Fun so far though

Old ABC2 was about learning follow through and overlapping actions. So in the chor with the ball floating back and forth it was just to concentrate on the whole thing as if it wasn't alive, but when the ball is alive and hopping around on it's own then the tail is also alive.
ABC2 A: Good start, the follow through looks natural, which not everyone catches on their first try. But when the ball changes direction it looks like the tail is changing all at once (all three segments change on the same frame). This is overlapping action aka successive breaking of joints. First the first segment should move and change then the second is pulled along into the change and then the third is pulled along by the second. The give away is that when the tail is passing directly underneath, it's a straight line. Also it looks like the first and last frame are duplicates, which puts a tiny lag in the animation (when animating a cycle I usually set my first and last frames the same so the animation will go to the same place, but I render up to the frame before the last so the viewer doesn't see the last frame twice.)
ABC2Bver1: So here also the ball is not alive so the tail is also not alive.
Your doing a good job of keeping the consistency of the tail, it is always about the same amount of stiffness, it's stiffness doesn't very (which it shouldn't). Again there's the straight down tail as it passes, the joints aren't being animated successively. The diminishing of the wiggling is good for when the ball stops (might be a tad biased on one side). You did a great job of the first joint of the tail not moving until a lot of pressure is pulling it (keeping your stiffness consistent.) The tail seems to move right before the ball falls at us, instead of being pulled by the ball. The first impact with the tail is pretty good actually. The tip should be jolted downward though. But after the first impact the tail segments should be more affected by the ground, as gravity pulls on them and they get impeded by their attachments to each other.
I'd suggest you try animating a looser tail, just for variety. One trick for animating follow through is to animate the top joint first and hide the rest, then once the top joint is animated unhide the next and animate that in relation to the top joint, then on down the line the same way. A classic follow through excercise is to animate a reed of seaweed sticking up and floating back and forth in the tide (you could just make a chain like this tail of cyllendars with bones). Often when talking about follow through you hear the term "whip action"
Great job working on all these excercises. Hope my critique's can help you improve.
-Alonso