Obviously you have to turn on Friendly Fire in the Options first before attempting to unlock this achievement.
A couple of things you should prepare for before attempting this achievement that will make this very manageable alone with 2 controllers, but it will take some time to play through this. Here's what you have to do.
1. Play through the game as you normally would until you have reached or finished Double Dragon difficulty Solo, whichever you do is fine.
2. During these couple of runs to reach or finish Double Dragon difficulty, make sure you have gathered enough mythril and money to max out the following Stances and Sosetsitsu mixtapes to level 50 for a painless journey through the co-op mode.
- Training Wheels (recommended for boss fights)
- Spin Kick (it's for boss fights so you can avoid some attacks)
- Dragon Swarm (highly recommended, it's a full-screen enemy sweeper)
- Magic Gambit (this is for spending less magic on your Sosetsitsu)
- Lightning (there's at least one area where this is useful)
3. When you are ready to begin, pick Continue on the Player 1 side of the Play screen and load your save file, while on the Player 2 side, pick Shadow Bro, then select Double Dragon difficulty once that's done.
Now here's a very good thing for everyone to know. You do NOT have to play through this mode from start to finish and then fail midway to start all over again. You can play through each stage one by one, and as long as you have survived with both players through each stage and then the game saves your content after each stage, it will count as a full completion. So you should just go through each stage carefully, and then when you beat the stage, let the game save your progress and then you can continue with the next stage you reached.
There is at least one thing that will void this achievement from unlocking. If at any point that either Billy or Jimmy loses all their 1ups so that the text under their life bar says "Hold
: Steal!!", it means that you have to start that stage over again by either going back to Stage Select, Title Screen, Dashboard, any of those will help you, so you can then go back to the stage where you died and try again.
You should have a pen and paper or other kind of tracking tool so you know what stages you have completed during your co-op run. Although you can finish each stage in any order you want, it's safe to start from the very first stage and all the way to stage 10, because this will work guaranteed.
Now for overall specifics for each stage and some moves you have to perform.
You should move Billy and Jimmy slowly forwards through the stages with both controllers using the
, and they should be close to each other if possible. Have as much health and magic as possible, and if you need health, press
on both controllers to do a Life Split between both the bros.
Equip Dragon Swarm and Magic Gambit. When a group of enemies show up, use Dragon Swarm, it will hit the enemies for high damage but not your partner, so it's a safe Sosetsitsu to use a lot. Also between each Dragon Swarm attack, press
to do a High Five that give you both Gleam. The gleam will fill up your magic bar quickly and also give you extra hitting power when you pound enemies if they are on the ground. Another thing about high fives is that, during the high five animation, you are invincible so make use of it if you are in danger and need to perform a Sosetsitsu move quickly after.
Keep repeating these moves, but do it after a second of waiting time. I can report that if you do it too fast, the game might freeze either at the beginning of the Dragon Swarm attack or at the white screen after the attack. So if that happens, you have to power off your console and start the console and game again from your last point.
Another suggestion is to try using high level (or max level) Spin Kick through each of the stages if you feel it's more comfortable to use,
Moving on, what you have to do during your run, if you stumble across 1ups anywhere in the stages, let the 2nd player (or the one that you won't use that much in boss fights) pick them up, so that the player will have a surviving chance when you are fighting bosses with your main controller. With your main controller, you should buy 1ups from the shops since you can't do it for the 2nd player if it's a Shadow Bro.
Any chance that you get, try to use the Gleam high five move with the
. It will give you a lot of punch-kicking strength and it will be useful against both bosses and regular enemies, specially if they are on the ground after you used Dragon Swarm. For the boss fights, just put the 2nd player in a corner, specially if that player has lots of 1ups, and just focus on defeating the bosses with your main controller. If the 2nd player falls down and needs "Help!", do all you can to quickly run over there and "rile up their tape" again so they can get revived before they lose a 1up. Also by doing this, they will have full health back again and then you can do the Life Split high five when you need health for your main controller again.
The Dragon Swarm + Magic Gambit works for pretty much every situation with a group of enemies on-screen, but there's one instance where you "might" be needing Lightning Sosetsitsu instead. That's at the beginning of Stage 9 where you are sliding down on the snow-slide section on the platform with groups of enemies falling from the ceiling. Make sure both Billy and Jimmy are facing each other, quickly use Gleam high five if you have to, then keep mashing
on both controllers to spam Lightning on all enemies, and they will die quickly or fly off-screen. Don't use the move too much tho, because if there's no enemies on-screen, the Lighting will hit you instead. Keep doing this move until you finished the snow-slide section, then change back to the safer methods of dealing with enemies from this point on.
When you reach any stage with rockets flying towards you, have your finger(s) on both
of your controllers and keep rolling to the right of the screen to avoid all the attacks with minimal damage and casualties.
Make use of all the shop locations in each stage, and buy much lives for your main controller if you need them. The Stage Select gives hint on where shops are located and you can find them among the background in each of those stages if you look closely, or fall down a platform with a arrow marked next to them. Also during my run, I brought Fuzzface with me from stage 6 and he will help you when there's no danger and when you need more health.
Keep advancing slowly towards each stage, making sure the game saves between each stage and once you beat Skullmaggedon and Evil Marian and then jumped into the heart portal, the achievement will pop. When I reached this boss fight, I had 9 lives for my main controller and 7 lives for the 2nd one. I ended up with 6 lives for the first player and 3 lives for the second player after the fight. If it didn't pop yet, then go back to any stage you missed and it will unlock at the end of any area you have finished with both your bros surviving.
I hope this helps everyone! Please send a note if you need more detailed help.
Happy Hunting, TA friends~ ^u^