Ok, here goes, as you know, when ditto attaches energy onto it, it becomes
the kind of energy it needs to use as the defending pokemon.
But what happens when it transforms into Blastoise and uses raindance?
You see, the problem is that once you place an energy other than water, it
becomes a water energy on ditto. Thusly it doesn't count as one energy per
turn. On the other side, the act of playing an energy other than water on
ditto counts as one energy per turn and is not considered water energy. I'm
pretty sure you cannot use raindance on energy other than water, but still,
knowing everything about the rules does not help. So what do you think? Love
your site. From the infamous Mew3, master deck builder.

The Rain Dance power must be announced when you playing the Energy.  Thus, if the energy in your HAND is not a water energy, then you can not Rain Dance it. 

Scott