The consequence that is intentional is:
Spanish conquistadors bring their horses with them across the Atlantic. Some horses escape or swim to shore after a ship sinks. The Plains Indians become expert horsemen and buffalo hunters.
The intentional action here is the Spanish conquistadors bringing horses across the Atlantic, which was a purposeful decision to aid in their conquests and colonization efforts. The resulting adaptation of the Plains Indians to become expert horsemen can be seen as an indirect consequence of this intentional action.
In contrast, the introduction of rats and the consequences related to disease and extinction are unintentional consequences of their transportation aboard European ships. Similarly, while Columbus bringing pigs provided food, it was likely not an intentional outcome of bringing the pigs specifically to support the growing population; it was more of a side effect of their introduction.