Project Spark

This is actually pretty easy.

First off, you want to play and level up Scarlett to about 5.

Once she's on level 5, she should have a charge attack that locks onto nearby enemies by holding X. That's the key to this. So now start a new Crossroads game, and select Scarlett and put the difficulty on easy. You can pick whatever settings you want.

When the game starts, talk to the quest giver and then pick Goblins for the enemies, because they cannot shoot. So kill the 3 that appear, and talk to the quest giver again. You should now have to place down the boss location. Put it as close to your village as possible, so that enemies do not spawn on the path. Now go and talk to the quest giver at the boss area. He will have you select more enemies to face before the boss. Again, pick goblins so they can't shoot you, and use the D-Pad to lower the number of enemies. Once they are defeated, you will have to pick a boss. This is the hard part. The easiest bosses for this I found were the Flame Knight guy and the Box of Squirrels. You can keep pressing X until one of these comes up. For the Squirrels, just keep running around holding and releasing X, until they all die. Try not to run toward walls, or turn too sharply toward them, because they're quick and will hit you if you do. The Flame guy is also pretty easy, his only problem is his projectile attacks. But, if you stay back far enough they are pretty easy to dodge by jumping or rolling out of the way. And just keep using the same charge attack because you don't have to be facing him to hit him with it.

Once you've killed the boss, collect the chest and return to the town quest giver. An exit portal should appear, just go up to it and exit. It will have a stats screen showing the amount of damage you took, and if it's zero this'll pop!

If you have Hakkon unlocked as a playable character this is a breeze.

At Level 3 you unlock a special ability (requires you to press the "y" buttom) that summons an ally who throws an arrow at the enemies then disappears.

With that said, just start a crossroads adventure with any setting, choose Hakkon as you champion and only use the Y button attack to defeat the enemies, and keep running from them as you do it, you will have no problem avoiding being hit.

As for the Main boss, I just chose the squirrels, they dont have any ranged attacks, so I just kept running from them pressing "Y", it's very easy to avoid being hit that way.

This is a fairly easy solution, I did it in my first try!

An extremely easy method I found will take you a matter of seconds.

Play as Conker, always choose Goblins as your enemy and make sure the guards are the lowest amount (2) and Goblins. Make your way to wherever the boss fight is going to happen, randomise it until you see the yeti.

The yeti can only use melee attacks and gets locked into a damage type animation every time you hit it. Using the SMG you can knock him back as far as possible without any danger of being hit.

Kill the yeti, finish the quest, exit the level and boom, 10G

**ChooseMyFate also stated in the comments that if you choose the fortress you can stand on the upper levels of the fortress where the Yeti cannot reach you**

Create a crossroad gameplay with village and enemy location nearby.
Use Seph at least Level 10, remember to select easy mode while choosing the hero.
Choose only Goblins as enemy and only 2 guards before the boss.
So you need to kill only 5 enemy before the boss.
Choose Yeti as boss.
Stay at long distance and shoot him pressing X for a few second, then he
will try to reach you, or he will throw ice balls.
jump and escape to avoid it, then hit him with long distance shoot.
Keep doing this for 2-3 times. Do not risk, is better avoid him a little longer then risk to attack while you are not in a safe position.

I don't think this achievement is. Valid anymore
I have done this 3 - 5 times now and still ain't got the achievement before the 12/8/16.

It's a shame they had to bring the servers down.