Mario has bunkered down atop a hill with his trusty gun as his only ally. The enemies will come at you from the left and you must mow them down before they reach you. Each kill will net you cash relative to how difficult the enemy was. For example, the basic ground undead are worth $10 while the speedy Goombas are worth $75. You will need to purchase Sonic the Sniper for $1500 after you've saved up enough cash (should be ~level 5).