That smile…well, it may have been a smile, but it was as expressionless as a mask; it may have been a smile, but it was cold and callous through and through; and—because it was a smile—it filled anyone who saw it with endless terror. It was that kind of smile.
WHAT A CREEP
～である to be a~ (mostly used in writing)
～ながら while (～でありながら while being a ~; despite being a~)
～のように like a ~
無表情（むひょうじょう） expressionless (無 not + 表情 expression)
何処までも（どこまでも） anywhere, as far as possible, completely, thoroughly (どこ where + まで until + も also = wherever you end up looking, it’ll be this way there too)