Easiest way to complete the hardest ones(Pacifist, unlocking 2nd char, 3000m on rocket) is to not buy any powerup but the rocket. Just save up for 3000 coins, buy the rocket and it then becomes the only powerup you'll see. Getting 2 in a run becomes very easy and makes unlocking the 2nd character a cinch. A powerup should spawn very early in the run which also makes getting Pacifist about as easy.
Do that and the other quests become unlocked on the way to saving up 3000 coins anyways.
I feel like this game almost punishes you for buying upgrades other then the rocket. Many of them cause the game to lag just long enough to make me miss the platform.
I have problem with ,,Unlock-her"? How to unlock this quest?
You have to free Girlbot, like how you got Armybot. As you're playing something on the screen should pop up telling you how far you have to go to get her.