Complex sentence: It has been seen that he cannot talk except for a few words (although Harold seems to understand him just fine) and he cares for Mina a great deal but tends to cause mischief that yields supernatural consequences.
Split into simpler sentences: It has been seen that he cannot talk except for a few words (although Harold seems to understand him just fine). He cares for Mina a great deal but tends to cause mischief that yields supernatural consequences.