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Jon Irenicus, Shattered One is a legendary card that, at the end of your turn, gives control of up to one of your creatures to a target opponent, taps it, adds two +1/+1 counters to it, goads it for the rest of the game, and it cannot be sacrificed.

Serendib Djinn is a creature that, at the beginning of your upkeep, sacrifices a land. If the land is an island, it deals 3 damage to you. When you control no lands, it sacrifices itself.

The strange interaction happens when you donate Serendib Djinn to an opponent using Jon Irenicus, Shattered One's ability. Once the opponent controls no lands (usually by them being sacrificed or phased out due to something like a donated Taniwha), the Djinn will attempt to sacrifice itself. But, it can't due to the effect from Jon Irenicus.

This loops forever, permanently, and can never be stopped in Forge. The game is permanently locked and cannot continue, as the ability immediately adds itself to the stack over and over.

Damage175 wrote:Jon Irenicus, Shattered One is a legendary card that, at the end of your turn, gives control of up to one of your creatures to a target opponent, taps it, adds two +1/+1 counters to it, goads it for the rest of the game, and it cannot be sacrificed.

Serendib Djinn is a creature that, at the beginning of your upkeep, sacrifices a land. If the land is an island, it deals 3 damage to you. When you control no lands, it sacrifices itself.

The strange interaction happens when you donate Serendib Djinn to an opponent using Jon Irenicus, Shattered One's ability. Once the opponent controls no lands (usually by them being sacrificed or phased out due to something like a donated Taniwha), the Djinn will attempt to sacrifice itself. But, it can't due to the effect from Jon Irenicus.

This loops forever, permanently, and can never be stopped in Forge. The game is permanently locked and cannot continue, as the ability immediately adds itself to the stack over and over.

The thing is that this is not actually a bug. If this happens in paper game, the result will be the same -- infinite loop. If nobody can interrupt this loop, the game ends in a draw.

The first ability is an end-step trigger. A target opponent gains control of up to one creature, we put two +1/+1 counters on it, and tap it.