Humsz with cards like that you need to ask yourself...what are you cutting for it? If it is a thread, wouldnt you rsther always have the thread than to have a card that forces a specific card to be in your gy? There is a lot of exile based removal. Imagine a hand of 3 lands scales oxolith 2x recomision. This hand does nothign but if the recomission is even a worker you are golden. If it was 1 mana it could be better.
Couldnt u have forced the Tron players hand by putting the Ozo's single counter on the Rav, thereby puttin them into a catch 22? Either they kill it & now die to lethal attacks OR u keep the Rav, kill Karn with a split up attack & use/create ballista with the rest of lethal counters? :O
12:50 couldn't you have put the Ozolith counter on Ravage to either deny the block or deny the ping-romoval? Then if op pings you attack face and if he doesn't you split to kill Karn and then finish with Ballista.