A joke would be out of the question, simple condolences always sound insincere(and sometimes genuinely are), and I'm not nearly clever enough for flat sympathy to not sound like an insult.
It's worse than saying nothing because you know it will fall on deaf ears.
MKog got some bad medical news and I wish I knew how to comfort him. Not super serious could-die-tomorrow news, but looks and sounds kinda bad, going by the artistic depiction and his personal description.