If you want to go with the landmaster( tank ) in VS mode, you have to get the medal on Venom first.
To get expert mode you have to get all the 15 medals.
To get a nicer title screen, you have to get all the medals in expert mode.
If you lock on a enemy in a group and you hit this target, you will get a +3 hit bonus. This way you reach the number of enemies quicker to score a medal.