After messing around with it, I can safely say that the Hydrojab isn't useful. The hitbox on the jab doesn't last for long, so most of the slide is just empty animation, and you can get about as useful a slide with True Hydroplaning.
Letting go of the Control Stick after a shellshift basically gives you a decent slide while in neutral animation, sort of like a mini-True Hydroplane. Call me stupid, but I didn't realize that that's why people would repeatedly shellshift in place.
That said, just jabbing at the end of a shellshift looks like it's an awesome move. It takes little practice to get used to the timing, you can get a decent slide before you start jabbing (which pretty much stops moving after the hitbox is out) and, depending on the timing of your jab, you can change up how far your slide goes, which makes it unpredictable by itself, given that you can control the spacing quite well.
This is made really great due to the fact that the Hydrograb hitbox covers all the distances in which a jab out of a shellshift would hit people, as well as puts Squirtle out of range of retaliation if the grab misses, due to the Hydrograb's long slide. If they spotdodge or roll toward your starting position, they're far away from you. If they roll backward, you get to punish, unless it's, like, Lucario, but, his moves are so slow otherwise that you won't get punished for it.
On top of that, either option can be made unpredictable through shellstalling, with both commands being really easy to do consistently, and both benefiting a great deal from it. People with awesome Up-B moves and Up-Smashes out-of-shield will be reluctant to use them to get around this if you start shellstalling. It is a super-safe bait, and it makes your actual attacks virtually impossible to read.
The jab is mostly to stuff people who are trying really hard to approach and to keep people out of your personal space. It also serves as a bait, making people try to shield the jab, only to get grabbed. The Hydrograb is what would be dealing damage, as it sets up for juggles and is a fantastic option that negates the usefulness of shields against Squirtle's many pokes. If your opponent wants to try to attack you before your shellshift is over, you can always jump out halfway through or simply shield at the end of the shellshift.
Given Squirtle's amazing walk speed and the versatility of his shellshifting, it's easy to put yourself into position for this at any given moment. The Hydrograb has enough distance on it to make it a potentially offensive tactic, and you do move forward a little overall after a jab. However, this seems REALLY useful defensively, and gives Squirtle a great boost in camping. I think we should analyze this stuff and see what distance from the opponent would give us the most control.
If Squirtle is going to keep the lead, it looks like this is the way to go. Perhaps this is the ticket to timing people out with PT.
