Real Steel

Credits to microroyc for posting a solution, but I felt a more detailed one would be helpful. First things first: go to the DLC menu and grab the free pack at the bottom. It contains three helmets, one of which (Regal Head) is good enough to use throughout the entire game.

Just like in Underworld, most of the opponents in WRB will be a cakewalk, with a few of them acting as sudden roadblocks. When you hit those roadblock opponents, you will need to go back to earlier fights and grind XP so you can buy better gear.

Here's how to level up each skill easily:

Offense: Just go against an easy bot and pummel him with forward+Y/X. This skill will level up nicely in regular matches without much grinding needed though.
Speed: Just hold LB and keep dodging attacks for as long as you can. Each dodged attack is 70-150 Speed XP. Kong is a good bot to dodge. (If you have Speed 30 and want to raise it even more, you can buy the Agility Modulator (or whatever), which lets you dodge even when you're out of energy.)
Guard: Same as speed, just hold RT to block attacks for as long as you can last. Kong is good here as well, or Metro.
Performance: The easiest skill to level up... Simply mash your d-pad when your opponent is knocked to the ground, performing as many taunts as you can while he's down. Taunts give performance XP. I use the "come here!" taunt as it's fast and spammable.
Destruction: I just bought the Super Hook tech move and used it at the beginning of every match, and as often as possible throughout them, and my Destruction skill is almost as high as Performance, so there should be no need to focus on leveling this.

Note: you do not seem to gain less XP for fighting easy bots, so go ahead and fight the very first few ones for all your grinding needs.

And that's really all you need to know. This game is very simple to beat, and you don't need to be a master boxer to do it. Just keep your BR up by buying all new gear whenever you hit a road block, then just go in and spam tech moves and random punches and you'll win with ease.

One very easy tactic is to get the opponent on the ground in any way you can, then just spam the Super Hook tech move as he gets up. After he goes down a couple of times, he'll get knocked right back down again when you Super Hook him right after he gets up.

My BR when I beat Underworld was about 3500 and it was not a problem that Zeus (the final opponent) has 5800. If he poses a threat, just use the Super Hook spam manouver in the below video. Another tactic that works wonderfully is using paced forward+Y/X punches; not spammed as you'll run out of energy, but well-timed and constant. The AI doesn't really know what to do if you keep punching it in the face. (Video credit to Roy Combs.)

This achievement can be done fast but it is not reccomended. If you don't plan on playing online much and just want the cheevo, then do the following:

1: Save up a little money and buy the Super Hook tech move(you could also buy the rolling uppercut it can be very effective)

2: Build your bot to have atleast decent: power charge, attack, and power recovery.

3: When you are fighting your opponent stay a full screen length away from them and use the Super Hook tech move. it will do a decent amount of damage and be almost always a sure hit.

If the text didn't help much here is a video demonstration.

If you have the cash to blow on microtransactions, you can buy a pre-made robot, which saves you from any grinding.

Best one is BESENJA with a rating above 8000. Costs 800MSP. Every opponent goes down in about 3-4 hits.

This game is the prime example of pay to win. Only should be done if you've had it with the ridiculously unbalanced AI.