[quote=@Phoenix]
Typing is somewhat irrelevant (any type can learn to withstand any weakness, but this must come at a cost). 

Pokemon may have and additional type added to their species. They may also have types omitted. This goes for Pokemon moves, as well.
[/quote]

Would you mind elaborating on these two points please? With these and the rule governing types of moves a Pokemon can know, I'm having trouble understanding the level of importance of types.