Complex sentence: Taunting Saotome, Manticore decides that it would rather take his form, but it stunned when, rather than begging for his life, Saotome explains why Yurihara's form would be more beneficial to Manticore, and confesses his love to it.
Split into simpler sentences: Taunting Saotome, Manticore decides that it would rather take his form. But it becomes surprised when, rather than begging for his life, Saotome explains why Manticore would find Yurihara's form more beneficial, and confesses his love to it.