@Random: Apologies, but this might put a damper on Mercer 'staying in character', as it were...
As Mercer walked through the barrier with reckless abandon, he found himself impacting a magenta wall that rapidly formed, then he was covered in black flames that burned far hotter than any mortal flame. Due to his incredible amount of stored biomass, he wasn't immediately incinerated, but he felt himself losing mass quickly as the flames began to consume him. However, for what it was worth, he was past the barrier.
Those who approached the building would find that the entrance had massive, 20 foot tall doors. The doors were already wide open, showing a long corridor dimly lit by candles that hung from the walls.
The whispers continued, urging everyone to enter the building, they grew louder, but still sounded soothing.