OK, the Wikipedia article JacobPast177 linked, though, seems to indicate that Modern Standard Greek has this mediopassive form, that includes not only what one would consider deponent in Ancient Greek, but also the middle voice. Honestly, I just wanted to know whether there were just some fundamentally different conjugations in the indicative active, and to see how this thing was conjugated.
Yes, you are right, my fault. Θυμάμαι has no imperative of the present tense (προστακτική του ενεστώτα), i.e. of the imperfective aspect, so the subjunctive of the present tense (υποτακτική του ενεστώτα) is used instead. I hope I'm getting the grammatical terms right, since I mainly learned Greek here in Greece just by talking to people, and only a little from textbooks.