1~There is no need to defeat all enemies, you can save time by passing them.
2~When fighting with the boss, just pressing the button RT to charge the kick ass. Increase your attack power.
3~You will get 19 achievements except graffiti and wifi by completing the game.
The distribution of graffiti and wifi is as follows:
1-1: 1 graffiti / 1 wifi
1-2: 2 graffiti / 1 wifi
1-3: 2 graffiti / 1 wifi
2-1: 2 graffiti / 1 wifi
2-2: 3 graffiti / 2 wifi
3-1: 2 graffiti / 1 wifi
3-2: 2 graffiti / 1 wifi
3-3: 1 graffiti / 1 wifi
4-1: 2 graffiti / 1 wifi
4-2: 2 graffiti / 1 wifi
4-3: 3 graffiti / 2 wifi
5-1: 2 graffiti / 1 wifi
Search everywhere you can go, you will find them.