My strategy is:
Begin with a Dual on far left and a Piercing on the far right.
As you earn souls, keep stacking Duals on the first column until you have 4 of them.
After that, build a Booster at the bottom.
Do the same for the 3rd column, leaving a space in between.
On the fifth column, stack Grabbers or for lower levels, Sticky with Perfume on top if you do have it.
Finally, stack Piercings on the last column and end with a Booster.
Most of the time, you won't get to finish this setup. Perhaps only on Survival, where you can set this up and keep whacking the bosses while pausing to collect the souls and re-setup your cheesed stacks. I beat Survival with 4 toys left :]
Don't forgot to change a Dual for Eye when necessary!
 "The Last Door - Chapter 2: Memories"){kind=icon}
 "Theme Hotel"){kind=icon}
 "Zomgies 2"){kind=icon}
 "Bullet Heaven"){kind=icon}
 "DJManiax"){kind=icon}
 "Toxers"){kind=icon}
 "Demons Took My Daughter"){kind=icon}
 "Robot Wants Ice Cream"){kind=icon}
 "Epic Battle Fantasy 3 Walkthrough"){kind=icon}
 "Monsters' Den: Book of Dread"){kind=icon}
 "Infectonator : World Dominator"){kind=icon}
 "Fly Hard"){kind=icon}
 "My Pet Protector"){kind=icon}
 "The Great Siege"){kind=icon}
 "Death vs. Monstars"){kind=icon}
 "Super Stacker 2"){kind=icon}
 "Shopping Cart Hero"){kind=icon}
 "Globetrotter XL"){kind=icon}
 "Perfect Balance"){kind=icon}