At the beginning of each of your up-keeps, you must sacrifice a land. If you sacrifice an Island this way, Serendib Djinn deals 3 damage to you. Then when you control no lands, sacrifice Serendib Djinn.
Honestly, if you play this guy at the right time, this Djinn can win you the game. There's really not much in Old School Magic that can touch him. So, while he has a big downside, he's not unplayable.
Djinns really were the boss monsters of Old School Magic. It's fun to how much the game has really changed - mostly for the better. But, Djinns are cool. It's too bad recent ones haven't been the boss monsters they once were. This Djinn carries a high price tag, due to being on the Reserved List, and a classic Magic the Gathering card.
Have you ever played Serendib Djinn?
~ Phoenix <3