  This paper contains the second part of a two-part series on the stability and
instability of extreme Reissner-Nordstrom spacetimes for linear scalar
perturbations. We continue our study of solutions to the linear wave equation
on a suitable globally hyperbolic subset of such a spacetime, arising from
regular initial data prescribed on a Cauchy hypersurface crossing the future
event horizon. We here obtain definitive energy and pointwise decay, non-decay
and blow-up results. Our estimates hold up to and including the horizon. A
hierarchy of conservations laws on degenerate horizons is also derived.
