Ok well first off before you ask for tips your skills with Parappa will matter greatly. If you don't know how to make most of Parappa moves effective, combo off about any hit & a grab and use his speed (which I find faster then Raiden from my experience O_o) to your advantage then tips won't matter because your gameplay will be lacking and cannot compete. Soo?
I use all the moves beside like two of the grounded skateboard moves, I know how to ap burst from almost all the moves I'm juss still working out the timing parts I mess it up a little, I don't really use his speed effectively I guess? Juss to get in and avoid supers, I know his KCs I think I'm pretty OK I'm getting better but I juss want general strategies against ratchet like use forward square or mic to punish his landings juss stuff like that
Depending on the Ratchet player's playstyle the skateboard slap comes in handy because it reflects projectiles (which is useful then MOST people think). Anyway you want to get in close, which is why I stated speed is important. Parappa is a fast MOFO. If you know how to use his speed getting in close is your BEST bet, so you can nail your combo's. You wanna air short hop air dodge a lot and try to make it seem as your going to attack sometimes, but actually not. You gotta wait for openings, which is extremely hard for certain characters. If the player is skilled you want to avoid the KCs that he will try to pull off. Skilled Ratchets know that when they're applying pressure to someone and you're trying to get in to attack close, they'll get you with those wrench confirms when the time arises. Both his wrench throw and wrench swiping combo.
EDIT: As for the boombox. Don't heavily rely on this because Ratchet can just use his sniper. Although, there are a few things you can do. Whenever you choose to use the BB, you can use it and just block while gathering the AP while he gets chip damage/AP. I actually however, highly recommend you use this as a tool to get to whatever super you are on the edge of getting. So even if he is getting chip AP off of you while blocking you'd still get your super. It's better then risking the chance of him getting off a combo on you even if you get your wanted super in the end. Also you can use it as a "form" of decoy by using it then going back into battle. <--- Hard to explain that concept, but the rest you should get. There's multiple ways you can go about that.
Alright thanks ill take another look at using his speed and that skateboard slap I forget about that sometimes oh and yea I get what you mean with the boom box I do that all the time thanks man --- Psn ayycole I'm on the quest to be the best parappa.