2004-10-04 : The ability can be used on a creature without First Strike or Swampwalk but has no effect.

2008-04-01 : If a creature loses first strike after first strike combat damage has been assigned, it won’t deal damage during the second combat damage step.

2009-10-01 : Causing a creature to lose swampwalk is useful only during the declare attackers step or earlier. Once the declare blockers step begins, it’s too late to block the creature.

2009-10-01 : Urborg’s second ability affects only the first strike ability, not the part of the double strike ability that acts like first strike.

2009-10-01 : You choose whether the targeted creature loses first strike or swampwalk as the ability resolves. If the creature has both abilities, it will lose just one of them.