Despite being a series about animals, there aren't any dogs pictured in the entirety of Redwall. The only mention of dogs is in the first book. They are never brought up afterwards.
Cats are some of the main antagonists of the books, most notably Verdauga, Tsarmina and Gingivere in 'Mossflower.' However, in 'Redwall,' one of the protagonists is a cat.
Based on my memory, there aren't any assaults in the series. As a general rule, the books are light on post-kissing romance, and I'm fairly certain they don't ever touch on assault.
Although most of the books have an uplifting ending, some are more bittersweet or upsetting. There are usually epilogues that lend a hand in keeping the endings light.
One of the recurring characters, Martin the Warrior, is often seen as a ghost during dreams, appearing to characters who might need his help or advice. Other characters might appear as visitors during dreams as well, but usually not while characters are awake.
The only horse in the series is in the first book, 'Redwall.' It is attached to a cart which crashes - the horse escapes and presumably survives, although it is never brought up again.
The series as a whole features animals as a main cast, and there are often gruesome battles and fight scenes that usually end in the death of some participating party.
In 'Mattimeo', the titular character is a mouse child who gets captured by slave traders. In 'The Taggerung', the main character is an otter who was kidnapped as a baby.