In Mario Maker 2, you have the ability to create a level that is 10 sections long and two high, as well as a sublevel that can either be 10 long and 2 high or 10 high and 2 long, for a total of 40 possible sections. Each section is 24 blocks long and 14 blocks high, coming out to a grad total of 13,440 blocks. However, on the overworld, the starting and ending points have a minimum number of blocks that are required to exist and cannot be manipulated (48 in total). So, that's 13,392 total manipulatable blocks.
Mario stands at 155 cm, and a single block is roughly half his height, so we'll just say that they're 77.5 cm on every side. That's 465,484.375 cm^3 of whatever block is placed per space or 6,233,766,750 total cm^3.
Now, it's hard to really tell HOW the blocks are being destroyed, but since nothing remains of the blocks after the rocket is used, and there's no statement of atomization, we'll just assume they were pulverized. (214.35 (j/cc))
That comes out to 1,336,207,902,862.5 (1.3 x 10^12) joules, or Multi-City Block Level.
However, we can actually take this feat one step further.
While most blocks cannot share the same space, mushroom platforms and semisolid platforms CAN. Mario Maker allows for a maximum of five platforms to exist within the same space.
Therefore, this feat would become 6,681,039,514,312.5 (6.6 x 10^12) joules, or Small Town Level
Quite powerful for our little rocket. This then, of course, scales to Undodog as well, since it can undo the rocket's strongest reset.