your about to finish red/hard mode. you'd see Mr DoomBringer in the intro.. he'd spoken in a deep tone before he turns to look at you.

[-Mr DoomBringer-]: "...A visitor?... ..mmm.. indeed. ..I have slept.. ..long enough.. ...And I must admit.... I am curious, ..About your skills... Weapon... ....Come forth.. ..child of man... And. Die."

He'd appears from the spawn while holding his ban hammer, and he starts walking towards the path to your towers. Ready to destroy them..