Thermal composition fluctuations were explored with SANS in a homopolymer blend dPB/PS of critical composition mixed with different amounts of a symmetric diblock copolymer dPB-PS. Phase boundaries of various ordered phases including two critical universality classes and the Lifshitz line (LL) were determined. Strong thermal fluctuations lead to a non-monotonic LL, droplet and bicontinuous micro emulsion phases, and a reentrant two-phase region near LL with an upper and lower critical solution temperature and a double critical point (DCP). The expected doubling of the Lifshitz critical exponent y was observed approaching the DCP.