Mainz isn't a team for Dortmund to even get borderd about because they are not a top team in the bundesliga that will give Dortmund so many taughts on how they will be able to get ahead of them especially if Dortmund weren't having to prepare for a champions league finals, I'm very optimistic in the fact thst they would have been able to just get over Mainz but then it's very normal that they will rest key plays in preparation for the champions league and that will mean they may not gat to win Mainz but a draw will be a fair result that they can work with with the reason that they are preparing for the champions league.
The champions league is the big game ahead for Dortmund and I'm certain in the fact that it's getting all the priority attention from Dortmund because their opponent isn't a joke at all coupled with the level of experience which they have which can be seen as an advantage they have got over Dortmund hence Dortmund has to employ every of their best strategy to getting to win this game or possibly a draw so they get to proceed to the game of luck which is penalty shoot out.