Complex sentence: Since absorbing Limbo and becoming Dr. Strange's disciple Illyana's magic on earth has been considerably stronger, such as when she used spells she learned from Dr. Strange to destory advanced Sentinels.
Split into simpler sentences: Since absorbing Limbo and becoming Dr. Strange's disciple Illyana's magic on earth has been considerably stronger. She used spells she learned from Dr. Strange to take out a bunch of advanced sentinels.