The Encounter Monster is a good idea, but I don't know that you really need new rules for it. It's more like a special application of the existing skill check and encounter trap rules. Like an encounter trap, each "section" of the monster (or the monster as a whole) can be overcome by a combination of attacks, skills checks, and so on, much like what you described.
For example, some people want to know what you'd do if the PCs decide to fight this monster that's clearly out of their league. Well, they can AFFECT it -- the same way you can break an encounter trap's spinning sawblades with attack rolls. You can't really KILL it -- but you can win the encounter by hurting it enough to convince it to go elsewhere, or change its actions.
That said -- I love the idea to have a chapter about this in one of the DMGs, because that's exactly the sort of thing DMs could use for inspiration.
I keep thinking of Shadow of the Colossus, of course.
For example, some people want to know what you'd do if the PCs decide to fight this monster that's clearly out of their league. Well, they can AFFECT it -- the same way you can break an encounter trap's spinning sawblades with attack rolls. You can't really KILL it -- but you can win the encounter by hurting it enough to convince it to go elsewhere, or change its actions.
That said -- I love the idea to have a chapter about this in one of the DMGs, because that's exactly the sort of thing DMs could use for inspiration.
I keep thinking of Shadow of the Colossus, of course.