By the way, what are the things that humans would realistically do when getting a Crash Bomb attached to them? Here's my list(it involves a surprising amount of Leaf Shield):
1. Hot Potato. They may try to play Hot Potato with it and attempt to pass it on to you. It's usually obvious when they try to do this, giving you a lot of time to react and outspace them. You can try Jabbing and Nairing to annoy them while they have the bomb stuck, go for a possible FSmash if the Hot Potato plan is extremely obvious, or you can surprise them by letting them touch you, then doing a Down-Throw to spread the bomb on them once again. (Since Leaf Shield and Down-Throw go well together, I wonder if this sheds some light on the borderline useless Down B)
2. Shielding. They can attempt to shield it. If they do this, you can stay close and punish with a grab for the few frames that they are stuck shielding due to the explosion. Since this is revolved around grabbing, I believe Down B would help here as well. If you can catch them in the lag, you can Down Throw with your Leaf Shield once again for extra damage. If they are Link, however, they can just stand and disregard the explosion without much lag at all. I wouldn't worry about perfect shielding, since this would be relatively hard to time for a human. (Crash Bomb is horrid against Link anyways, so don't bother)
3. Take it Like a Man. They can take the 8% like a man and disregard 1. and 2, although they can't do this all of them unless they are really content with taking the damage. If you do notice that they are doing this constantly, try to add more attacks their way to prove that maybe this option is kind of bad. They'll lean towards Hot Potato or Shielding, where you can hopefully get your precious Leaf Shield involved in the fight. I really do think that Crash Bomb and Leaf Shield will make a good combo, but that's just me.
4. Ledge Invincibility. If they get hit with it while off-stage, they'll aim for the ledge for invincibility frames. You can edge-guard accordingly to make sure that they don't grab the ledge. You can edge-guard multiple ways. You can jump in with a Bair, Fair, or even Uair at high percents in order to gimp. You can try to use your Metal Blade in conjunction with the Crash Bomb as well. I'm not sure if Leaf Shield would go here, although I did here some people talking about gimping with Leaf Shield. (Probably too risky and ineffective)