I'll say what you are doing well first. I like that you didn't use bounce pads. Although quite useful, I feel like they are too predictable, and make it less interesting. That, however, is just my opinion. You also have a good concept of how to get the rocket to squeeze through the tiles.

Now for the longer part: what could have been done better...

You generally (I hesitate to to say always) want to interact with the rocket more with these, since having "close calls" is a great part of what makes kraddas (and ddas in general) interesting, since otherwise it's just watching the ninja just bounce around. This being a kradda with one rocket, it's more impressive if you interact mainly with the rocket that's being kept alive, since that is the only enemy there.

As far as accomplishing this, I would say to firstly slow the pace of movement way down, or at least that's what I (try/tried) to do in my own ddas to get close calls and make things generally more interesting.

This helps in a couple of ways:

1) It's a lot easier to focus on what's going on for the viewer. It isn't necessarily bad in ddas for the player to move quickly (in many cases it adds excitement), but in the case of kraddas, the main enemy is the rocket and therefore you generally want to keep the player and the rocket close. This then comes down to a logistics issue: since rockets can only move so fast, this limits how fast you can go. If you go too fast, then you begin to simply outrun the rocket, and the viewer isn't focused on it anymore once it's far away (since they'll usually be staring at the ninja since that's where the action happens).

2) With slowing down, the rocket can then have close calls with the player. Of course, this simply adds a bit of tension and intrigue as the player narrowly escapes death. I feel that a good way of getting close calls is to play-test (likely frame by frame), run it until you die, then focus on a way to alter your path just enough to miss some way. It sounds a bit silly having written my process down haha

3) Having these close calls with the rocket itself helps in two ways (that I can think of). For one thing, it forces the rocket to start turning around the player. In my opinion, this makes for a more aesthetically appealing movement of the rocket, having loops and swirls around the player, instead of simply in a straight line in the direction of the player halfway across the screen. Secondly, this gives a feel of the player out-maneuvering the rocket, instead of running from it, which makes for a more interesting experience.

4) This last one is mostly based on my own opinion (or at least much more than the past three). I feel that having a slowly paced dda shows a kind of maturity and finesse with the author. It's very easy to make the ninja go quickly, but it requires a certain amount of control to make it go more slowly with good close calls and such.

Lastly, just a little note, once you are satisfied with how your dda is, then delete the rocket launcher and place it again. This leads it to be "created" last, and therefore appears above all other objects (except tiles, of course). This is just so that it is easier to focus on the rocket interaction.

And with that, I close my critique and advice. Take it for what you will, with grain of salt, perhaps on the rim of a martini.