This build is not viable in Survival mode (Calliope doesn't exist there) and is considered an advanced, micro-intensive strategy for the campaign on 500-800% difficulty. 1. What is Calliope? Calliope is a steam-powered, rail-bound artillery unit. She moves on pre-laid tracks (which you build like walls) and fires explosive shells in a wide cone.

You love micro, hate mass unit management, and have memorized zombie aggro ranges. Avoid if: You prefer static defenses or are playing Survival mode.