Ok, first off credit goes to ADIDA5 A55A55IN for helping me match up with some other folk, which in turn got this idea going.
The easiest way to get this is to boost it with 1 (or more) other people. Here's how:
First make a super crappy shadow. Just get owned by Jago in the three matches, you don't have to even throw a punch. I did like to taunt though just to make Jago attack me. Why? Because your shadow is super easy to defeat this way!
Second, you and your friend both use your daily challenge to challenge each other's shadow. You should win easily! Don't save your data as it will keep your shadow weak.
Third, keep checking your bounties, a loss gives you a chance to fight that opponent again. Even if it was from a bounty win before! So this means as long as you don't lose, you and your friend(s) can just keep doing bounties back and forth as long as each are on. Since you have two games, you should in theory almost always have one to play against your friend.
Rinse/repeat til your shadow gets 100 matches. If you happen to lose a match, you can always start again the next day with a fresh set of challenges towards each other. Just do it online at the same time and you can knock this out over a few hours!
Credit also goes to ScorchPSO and Stifler4Life as they were the ones who happened to be online whilst I was challenging them and we had a nice run of 40ish games back and forth!
Edit: Just so we are clear, I tested the weak shadow on a dummy account. My shadow and those I mentioned in the thanks don't have dummies that do nothing.
However if you do fight my shadow it is a weak representation of me. It always does medium combos and is pretty weak against sweeps and throws. But please save yourself the headache and don't fight it
You can do this with a local dummy, but trying to play 200 matches (maybe 199) by yourself will take longer than one good boosting pal.