Kekoa - Punch Kekoa until he dodges your punch, then dodge his punch back and continue. You can beat Kekoa with a FaceBreaker this way.
Steve - When Steve disappears to teleport immediately use your breaker button and hit him while he is invisible. Steve will be stunned for a moment allowing you to punch him once or twice. He also tends to change the rhythm from fast jabbing to hooks. When he is throwing hooks don't chase his punches, wait for him high or low as he will most likely continue to switch high and low.
Ice - Ice is a tough fight but he is quite predictable. He has a tendency to punch low so the best thing to do is defend low with dodge and wait for an opening to throw Ice in the corner. The use two hooks and a BoneBreaker followed by a HayBreaker.
Sparrow - She is a tough to fight toe-to-toe because she uses a very smart strategy (two jabs followed by a parry), however she is easy to beat once you realize she will dash-attack you constantly. Punch her with a hook and run away so she try to dash-attack you and defend here attack with dodge or parry. If you dodge her punch and hit her you'll have a few seconds so you can connect one more punch followed by a BoneBreaker and a HayBreaker. Run away after connecting the last HayBreaker and repeat the process. Be patient, she sometimes tries to trick you with the dash-attack by not releasing the punch right away.
Voodoo - Don't get hit his halitosis attack. Dash back to avoid being hit. Voodoo always throws his bad breath at you when you miss with a HayBreaker. You can normally escape if you dash back in time and have enough space behind you. If you get poisoned by it try walking back if you have space or mash buttons as fast as you can. Corner Voodoo with throws and in the corner use the same strategy Sparrow uses namely punch- punch-parry. After you punch him twice stop and charge a hook and Voodoo will likely punch into your charge and you will dodge him giving you the opening for a hook followed by a BoneBreaker also followed by a HayBreaker (if your character is fast). Learn this strategy well as it will be very effective against other users and AI characters.
Romeo - If you beat him on Fierce, you should be able to use the same strategy in Truculent and Impossible. You can chain 10 parry-parry-punch exchanges to get the combo meter to FaceBreaker level and finish it off with parry- parry-punch-FaceBreaker. BTW, this is a good fight to win the Untouchable achievement/accomplishment.
Spin - He is basically the same strategy as Sparrow but he is way harder. You will likely be hit with a SkyBreaker or FaceBreaker if you try to fight him toe-to-toe because he is so fast. With Spin you have to wait for him to dash- attack you then you dodge his punch (patience, he is even more tricky than Sparrow) and follow up with a hook a BoneBreaker and a HayBreaker. Wash-rinse-repeat. BTW, he will always try to dash attack you after you hit him with a hook or a breaker if you are far away enough.
Brick - Any time there is separation between you and Brick he will try his Stomp attack. Anytime you hit him with a dodge or parry hook that gives you separation dash attack him immediately and you will likely hit him in the middle of the Stomp giving you a chance to punch him again and do a BoneBreaker followed by a HayBreaker. If Brick's back is on the ropes you should run away to the opposite corner and dash attack him when he is about to get close enough.
Kiriko - Same strategy as Romeo but with dodges. Keep the L-stick pointed at Kiriko all the time to close distance. Once she is on the ropes you will be able to pull a FaceBreaker on her after a dodge punch.
Molotov - With Molotov you have to control space correctly and know the range of his HayBreaker. Charge a hook and walk back and around the ring (use all the ring). Hit molotov when he misses his HayBreaker and follow that with a punch a BoneBreaker and a HayBreaker. This should give you just enough separation so he will try his HayBreaker again. If you continue charging a hook and walk back and around the ring he will walk forward to try to catch you and he will try his HayBreaker at the edge of his range giving you the chance again to repeat the process. If you are cornered, don't panic, hold high (or low) and wait for him to punch you. After you dodge his punch and hit him with the hook use the throw button to reverse the positions and start walking back again. If you do this right you can win The Best D is a Good O achievement/accomplishment on this fight.
Socks - Socks is relatively easy to beat in the corner, especially if you use the punch-punch-dodge or punch-punch-parry strategy. He is really hard to fight in the middle of the ring so the easiest way to corner Socks is to dash back into your corner and use throw to reverse positions when he is getting close to you.