Time to revisit this....
Multiple Heads (Ex): Each of a rain dragon's two heads can take a standard action each round. Thus, it may make two bite attacks, use two breath weapons, or any combination of the two each round. It adds its Strength modifier to damage for its snake head, and 1-1/2 times its Strength modifier to damage with its jaguar head. Tlalocoatls can attack with both their heads at no penalty, even if they move or charge during the round.
or
Multiple Heads (Ex): Each of a rain dragon's two heads can take a standard action each round. Thus, it may make two bite attacks, use two breath weapons, or any combination of the two each round. It adds its Strength modifier to damage for its snake head, and 1-1/2 times its Strength modifier to damage with its jaguar head. Tlalocoatls can attack with both their heads at no penalty, even if they move or charge during the round. A tlalocoatl can only use one spell or spell-like ability each round. A tlalocoatl only gets one move action each round.
or
Multiple Heads (Ex): Each of a rain dragon's two heads can take a standard action each round. Thus, each round it can take 2 standard actions and one move action or one full round action and one standard action. It adds its Strength modifier to damage for its snake head, and 1-1/2 times its Strength modifier to damage with its jaguar head. Tlalocoatls can attack with both their heads at no penalty, even if they move or charge during the round. A tlalocoatl cannot use its extra standard action to perform a move-equivalent action.
I think I'm leaning towards the third option. Thoughts?