AZRogue
Explorer
Kraydak said:So an immobilized (or otherwise utterly lacking in available movement), charmed guy can interpose himself between an immobilized succubus and an angry person on the opposite side of her. Yay! Lets not get into what happens if the succubus gets enlarged, or what happens if people want to interpose themselves without the benefit of charm... Note that wanting to take a hit for someone else comes up a lot in DnD.
If they don't have a power active or an ability for it, then I don't think they can. Unless it's an option in the Combat chapter of the PHB, which it might be considering how many creatures use some variant of the ability.