....This will be a long post.....And I won't even list all the reasons....
Perhaps it is my Puffs play style or the fact I have a friend who mains Olimar that influences my opinion, but I'll start with several things I dislike about CS:
The first transformation-> It's just too damn small. This part is like Yoshi's but worse. And you start near your opponent. I don't like how quickly they can begin to pressure you. The positions of the platforms really hinder Puff in most matches and side KOs seem too easy. Now granted that helps Puff, but she can go farther off than most characters so IMO it hurts her more than it helps. Plus, smaller horizontal DI ability can be just as bad if not worse than a lower amount of vertical. Also you can't mind-game rollout. Now some Puffs say WTF rollout? But it still works because people are dumb and we know it 100x better. I got 2 BS rollout kills on Zero in one friendly match at Xanadu for this reason. I also got multiple ones on other people including tournament (singles). Plus it favors most top tiers/likely to see in tournament more-so than parts of Halberd. Especially Marth for example. Well aside from his utilt (F the Usmash we shouldn't ever be hit by that).
2nd transformation-> It's huge yay plus for Puff. But rollout is worthless and you can''t edge guard because there are no edges... And if your opponent is good you really don't want to go up to the top platforms escape pressure because now you're dead. Same for going outside the middle kinda.... Plus the statues get in her way. Overall it generally favors other characters more than her especially Olimar.
3rd transformation-> YAYYYY Falco's lasers it's Lylat all over again. Stupid tilts... Now you run to the ledge. If you aren't dead yet you now just gave up the stage while at a high percent. For most characters this wouldn't be the case though and you should be fine. Also, I don't enjoy sniping tilting ledges with rollout ever so I'd never use that as a recovery mixup here. There isn't much to complain about this part though as IMO it's the best of the three.
Now Halberd:
1st part/opening: Hardly lasts. Pretty negligible. Not much will/should happen. Unless down throw works if timed for the transformation to kill and only they die? Never tried it because I'm lazy/forget to bother. I know it works for MK. But that shouldn't ever really happen, but neither should a lot of things. If they tried to apply pressure you can always wait near the edge. Why/what character would gamble going closer to the edge vs Puff when the stage is about to transform? Nobody except MK. And if a different character does you have a gimp opportunity more-so than them for the reasons they do and the stage being about to transform. Don't forget footstools if need be.
2nd part: Hell yah. Sharking early because you have no percent. Guess what? You have no percent... Oh I said that already. Well it needed to be said again. Sharking is safe now against a fair number of characters to some extent and you can ledge camp/retreat/shark till you add percent to them. Really if careful, you shouldn't get hit much here/ever unless you are fighting MK. Worst case you use ledge grabs and the stage transforms and nobody really took any damage. If they stay on the top platform float through try to hit and get back to the ledge. And it's never fun for a Falco to try to recover here. Minute little plus there. Oh and if you get lucky and your opponent (not MK) trips while you shark then knock them off the stage and try to kill or try to read the roll and punish accordingly.
3rd part: Ok great now they have more percent than you. Well now you can utilize the stage interactions to your advantage to create/relieve pressure when possible in addition to giving a chance to even hit with rollout, rest, or another kill move depending upon how things go. You also might have done well enough on the 1st part that you get them to rest kill % and when you aren't at kill percent. These things aside this part is pretty much a neutral aside from the evil low ceiling which can now kill you.
Now it resets to part 2: Sharking may or may not be a valid option here now based on your %, but gimping them horizontally most certainly is. The platform won't help much though.
I'm to lazy to add more opinions/facts to any of this because A. It surely isn't all right as some of it applies more towards my Puff's play and B. This post is already to F**king long. Feel free to critique it. No really, feel free. I'm open to anything which can help my Puff improve at this point especially since there are no Puffs and the few that ever visit these boards seem to know her inside and out. Every tiny little mixup that one hardly ever thinks of like rollout bounce off PS1 windmill are incremental to her play after all.