Not passives. There are none in tp to avoid the anonymous culprit ("Mistakes were made") (but leaving the indefinite on "Somebody made a mistake"). Tense are covered, of course, by 'la' structures as are(probably) most other odd flourishes, though some would be better dealt with, maybe, by overt sententials : 'jan li toki e ni:' and the like. I suspect, however, that development of evidentials and the like will be before 'la'.
The real question sis, what class is 'monsuto' and that is just not clear yet. The current remarks seem to start it as a Noun, but those early notes do not always show the final basic notion. Based on the present stuff, though, 'mi monsuto' means "I am a monster" and 'mi monsuto e ona' means "I make him a monster" probably translated as "I fear him" (tough vampire and werewolf bites and the like are not to be discounted entirely). 'mi pilin monsuto' is "I feel monsterly" which seems to be "I feel ferocious" maybe angry, maybe powerful, maybe ... . But this is till deeply in the realm of pure speculation.