General Jarkeld

Text:

: Choose two target blocked attacking creatures. If each of those creatures could be blocked by all creatures that the other is blocked by, each creature that's blocking exactly one of those attacking creatures stops blocking it and is blocking the other attacking creature. Activate only during the declare blockers step.

Rulings:

• 10/4/2004 Does not undo any abilities which triggered due to the declaration of blockers. A creature which is switched away still has any triggered abilities resolve on it.
• 10/4/2004 The new blocker does not trigger any abilities which trigger on creatures becoming blockers, because the creatures were already blockers and the simple change of who is blocking does not trigger such abilities.