A Kangaroo's Best Friend 40
Defeated Bruce and freed Roo in Streets of Rage 3.
Either use the level select to get there straight away, or play through until you get to stage 3. After a while you will encounter a boss fight with a kangaroo (Roo) and his trainer (Bruce). You need to make sure you kill Bruce before you kill Roo. Bruce normally hides off the edge of the screen so go to the opposite side to entice him out and hit him with your hard attacks. Using the Japanese ROM will make things easier for you. This can be done with any character and will unlock as soon as Bruce is dead.
Imposters Need Not Apply 30
Defeated Axel’s imposter single-handedly with Axel in Streets of Rage
Play as Axel, and play through until stage two, or use the level select cheat to start there. At the end you will encounter Break, who is Axel's double. This is a pretty straightforward boss fight as he just has Axel's moves so you won't need to dodge much, just attack until he is dead. Remember this will be easier if you use the Japanese ROM. This will unlock as soon as he is defeated.
Ultimate Power 30
Max leveled a blitz attack in Streets of Rage 3.
You get a star under your health bar for every 40k points you get. You can either set the game to easy with 5 lives, and play cautiously through or you can use the cheap method.
To get this cheaply, simply load up level 6 using the level select cheat, on the very hard difficulty.
From the start, go left and down one floor in the elevator. Kill Gold and Silver then wait for the gas vents to turn on when the timer has run down. Enter the third door, and smash the crates inside for about 5000 points. As soon as you have everything you will be back in the original room. Go back in the room for another 5000, and rinse and repeat until the achievement unlocks.