Perception vs. reality. I recall that for this phase of the trial the person has to defeat herself. I think it only *looks* like the BigT we know and love, but is actually a version of what the trial magic has to work with, i.e., a modified version of LittleT herself. (Which is dire enough.) If I'm right, hopefully this version does not have fight skills better than LittleT.
@Lloyd: considering Lil Tir has advanced training techniques and memories nano'ed from the future, doubt FauxTirin would have better (maybe similar to what Lil Tir should have, or maybe a little better, but not near what Lil Tir has)