This trophy is awkward, but with a bit of patience you will get it. Here are some tips that works for me;
1) Find a sensitivity that works for you. You want something that feels fast enough that you can quickly move to deflect a fireball, but not so fast that you overshoot. For me, the default sensitivity was too quick so I lowered it to 4. I also used the D-Pad for this as I found the Left Stick way too unreliable.
2) Remember to hold "X" when you want to catch fireballs, which means you can aim where you want to release them. This is good for attacking enemies, but where is becomes immensely useful is being able to target your own wall with it when you don't have much wall left.
3) You wan't to take out the AI opponent diagonally opposite you ASAP. They are an absolute pain to quick kill and they have easy access to aim at your entire wall which means they can kill you easily once you have little to no wall left.
4) Get it down to 1 AI left quickly. It doesn't matter which AI is left standing last, as long as it isn't the one diagonally opposite you
5) Once there is 1 AI left there should be 3 fireballs on screen. If you have been lucky, the last AI has 1 opening to kill them. If their walls are still heavily fortified then you will likely die before you can get this trophy. If they have hardly any wall left then they will likely die before you can get rid of your wall. The game is so chaotic that you I couldn't plan for this. I just had to get lucky.
6) At this point, let fireballs hit portions of your wall that remain and even destroy your own wall yourself (Catch a fireball and aim it directly opposite the bit of wall you want destroyed providing it isn't at the corner of your base).
7) Lastly, once almost all or all of your walls are destroyed, you don't actually want to focus on killing the AI. By this time, the AI has probably lost most of their wall while you were losing yours. At this point, focus entirely on deflecting fireballs from killing you. Don't try catching them to fire back. Just deflect like crazy. Soon enough one will kill the AI whether it was aimed or not!