Urza block cards with the echo ability were printed without an echo cost. These cards have been given errata in the Oracle card reference; each one now has an echo cost equal to its mana cost.
May 3, 2019 · War of the Spark
A creature with horsemanship can’t be blocked by creatures without horsemanship. A creature with horsemanship can block a creature with or without horsemanship. (See rule 509, “Declare Blockers Step.”)
January 25, 2019 · Ravnica Allegiance
A creature with horsemanship can't be blocked by creatures without horsemanship. A creature with horsemanship can block a creature with or without horsemanship. (See rule 509, "Declare Blockers Step.")
May 1, 2014 · Journey into Nyx
A creature with horsemanship can’t be blocked by creatures without horsemanship. A creature with horsemanship can block a creature with or without horsemanship. (See rule 509, “Declare Blockers Step.”)
February 1, 2014 · Born of the Gods
A creature with horsemanship can’t be blocked by creatures without horsemanship. A creature with horsemanship can block a creature with or without horsemanship. (See rule 509, "Declare Blockers Step.")
July 13, 2013 · Magic 2014
A creature with horsemanship can't be blocked by creatures without horsemanship. A creature with horsemanship can block a creature with or without horsemanship. (See rule 509, "Declare Blockers Step.")
June 17, 2011 · Commander 2011
rule 702.30b not present in this release
April 1, 2011 · Duel Decks: Knights vs. Dragons
The phrase "Kicker [cost 1] and/or [cost 2]" means the same thing as "Kicker [cost 1], kicker [cost 2]."
February 4, 2011 · Mirrodin Besieged
The phrase “Kicker [cost 1] and/or [cost 2]” means the same thing as “Kicker [cost 1], kicker [cost 2].”
October 1, 2010 · Scars of Mirrodin
The phrase “Kicker [cost 1] and/or [cost 2]” means the same thing as “Kicker [cost 1],
February 1, 2010 · Worldwake
The phrase "Kicker [cost 1] and/or [cost 2]" means the same thing as "Kicker [cost 1], kicker [cost 2]."