Complex sentence: It was stated that there were 182 Xavier Institute students enrolled before M-Day (2006), after which they were reduced to 26, including X- 23 (plus Kid Omega in Beast's lab).
Split into simpler sentences: It was stated that there were 182 Xavier Institute students enrolled before M-Day (2006). They are now 26 including X- 23 (plus Kid Omega in Beast's lab).