The answer for this question has already been presented here.
Anyway I'd like to present my point of view.
What's the point in learning such sentences in an ironic way? These sentences should be said only when someone is in mourning. Otherwise, people will consider you a cold-hearted and impolite person.
May God have mercy on your soul. >> Que Deus tenha piedade de sua alma.
May God have mercy on you. May God have mercy upon you. >> Que Deus tenha piedade de você.
My condolences >> Minhas condolências. >> Meus pêsames.
It's easy to use sentences like that in an ironic way; everything will depend on the moment and the way you speak. But, remember this: it will very difficult to regain your friendship or even your bonds if you regret to provoke someone in this way.
If I realized someone speaking to me in such a manner, I'd would say: