NHF – new heroes for Heroes V 3.1.

By the way, a question: how does this artifact interact with Raileigh's special ability? -15% - 20% = -35%, or (1 - 0.15) * (1 - 0.2) = -32%?

According to the manual, most effects that modify initiative are multiplied. The exception is artifacts: their effects are added together, but multiplied by the enemy's Staff of the Underworld.
It remains unclear what happens with the +1 initiative bonus from a random Sanctuary, specifically, at what stage it is added.