The Eucharist is a profound mystery, and like other mysteries, by very definition, we cannot fully understand every aspect of it. For instance, how is it that the one, body of Christ with all of it's blood, can be given truly and factually upon the alters without exhausting it? We know and must believe as Catholics, the words of Christ... "this IS my Body... this IS my blood." But then one might as well argue about or question the miracle of the loaves and fishes, of which there were only five and seven (or however many), and which fed thousands.
Does Christ have two bodies, one glorious and one mortal? No. His one and only body was glorified. There is (to my knowledge) no distinction that can be made. Christ has not two bodies to debate between. So where is the question? Christ did not have a mortal body that withered and died in the tomb, for instance. That body is His one and only body, which is now glorified. So where is the confusion, unless one denies the resurrection?
As for being miserable and hurting oneself, there is nothing so blackly miserable as the torments and anguish of a soul wallowing in, and slave to, it's sins and vices. Yet there is no tortures on this earth that can deprive the Catholic soul of the hope of heaven, or the joy of the friendship of Christ, or the peace that comes from that knowledge. This person has clearly never visited a traditional Catholic seminary or convent. I recall in particular one convent which I visited when there was a traditional Mass being hosted there. Meeting one of the sisters, the joy and peace in her heart just radiated from her. And meeting or seeing various (truly) holy priests and bishops, one can see the peace they carry with them through all of their many crosses.
And as for penance, what poor soul who has had the misfortune of committing a misdeed, does not almost rejoice to pay for his crime, if he is sincerely sorry? The only way to misunderstand the concept of penance, is to misunderstand the concept of justice and personal honor (in worldly terms), by which a good man desires to see wrongs made right, and crimes paid for. But if atheism were so wonderful, why does the world, which is ever more atheistic, have ever more and more people killing themselves, now at record rates? So much for the joys of doing exactly what one wants, without conscience.
Of course, in a world where man has come to adore and honor only himself (and even then not truly, for if he did, he would live more virtuously so as to give himself more abundant honor), the concept of true honor (virtue) and penance (related to perfect justice) have become hazy at best, and in many minds and hearts utterly lost.
As for the Mass, however, it seems that this person thinks Christ had two bodies, and THAT... is what makes no sense at all. (Someone correct me or slap me or something if I'm just going crazy here in saying so.) The Eucharist is really, truly, physically the body and blood of the one and only Lord Jesus Christ. Under the LOOKS of bread and wine, yes. But factually, literally and physically they are not. They are really, truly and physically the body and blood of Our Lord, though all of our senses are fooled, so to speak. This is dogma (unless I have lost all right memory of it), and yes... a mystery... which is by definition something that the limited human intellect with it's limited human understanding is not capable of grasping. A mystery may be a stumbling block for a human being looking to put human limitations upon God's power... but according to the reality of God and His power, God can do anything, whether we can understand it or not.
But by all means, confirm what I have said, before using anything I've said.