Level 9: Thar She Blows!
Score 9,000,000 points - By this point in the game, it shouldn't be hard to maintain a combo (survivors!), aside from Grandma, who you may want to save the nailgun for.
Complete in under 5min - Rushing through the level isn't too hard if you use the nailgun effectively, and are able to quickly eliminate Grandma.
Save 2 survivors - Escort the survivors to safety!!!
Kill 30 Enemies with the Nailgun - Pretty much just after you pickup the nailgun you'll come across some hordes of zombies. Just use the powerful pickup to clear out the enemies.
Kill 20 Enemies with Father Bills pwnage - Father Bill's pwnage is an area spell that damages zombies near him - which should be beneficial in the large hordes of zombies on this level - and also heals any allies in the area.
Level 10: We're on a Boat, Mother$#@#er!
Score 7,000,000 points - There are a lot of bosses in this level, so you are required to have quite a bit of damage dealing ability, although there are a lot of weapon pickups. As usual, the biggest problem can be a fight with Grandma.
Save 4 survivors - Save the survivors after the boss fight. This is required for an achievement anyway, so you will end up saving more than 4 of them.
Kill a Damned Using a Melee Attack - If you've leveled up a melee attack, use that, or use Jeremy and his 4x damage Pwnage ability when a boss is nearing death. I personally find the Lumberjacks the easiest to melee effectively (from behind).
No Player is Downed - By no player, this means NOBODY including the AI. To do this safely, you will probably want to save the grenade launcher for the final boss, as well as your Pwnage abilities to quickly burn him down. Other than that, as always, the Gradma's will probably be your biggest problem and they should be dealt with quickly.
Kill 35 Zombies in the Propeller - The propeller is from a boat on the right side of the map. Guide zombies to it and watch them get chopped up into shark bait.