When it comes to the ground-based special moves, first, you actually have to take your opponent to the ground with a takedown move. In order to pull that one off you are first going to have to execute a takedown. Once you hit the takedown move be prepared to stop the bar in the middle of the little light blue tab. If you do, you will take them down. If you hit the dark blue you will get a “good” rating and if you don’t you will get a “missed” rating and will miss the takedown every time.
Once they are down, swipe down to execute medium strength punches and tap to execute jabs. If you have gotten taken down, then do the same thing – swipe down or tap. If you hit one of the green control moves, then be prepared to stop the bar in the light blue again. Repeat this until the fight is stood back up again.
If you do not want to use a fighter card to make a new fighter, you can use it to upgrade one of your current fighters instead. Rather than add that new fighter to your lineup, go instead to the training area, and tap the up arrow button next to the picture of your fighter. You should see the unused fighter card in here. Use it and apply it to your current fighter for a major experience boost.
A good reason to splurge for rare cards is that individual moves are not relegated to one or another form of rarity. There are common and rare forms of every move, so if you get a rare version of one of your moves, you can apply it for a gigantic experience boost.
Before you decide which of your standing attacks to upgrade to a high level, first, check their individual attack power. Usually, the most recent unlocks will have the highest base power, but not always. Upgrade the ones with the highest base level of attack power primarily, to increase their power to astronomical levels. You can kind of afford to ignore the weaker ones since the cards randomly rotate in during fights.
You can use as many boosts as you have available to you all at the same time. In general, though, try to save them for when you have one fight left before opening the big box. That is when the combined power of your opponent wil take a huge jump compared to the previous opponent, so that is typicslly when you will need all of that extra power.