Diamond City

This land enters with a shield counter on it. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)
{T}: Add {C}.
{T}: Move a shield counter from this land onto target creature. Activate only if two or more creatures entered the battlefield under your control this turn.

Fallout

Diamond City enters the battlefield with a shield counter on it. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)
{T}: Add {C}.
{T}: Move a shield counter from Diamond City onto target creature. Activate only if two or more creatures entered the battlefield under your control this turn.

Diamond City enters the battlefield with a shield counter on it.
{T}: Add {C}.
{T}: Move a shield counter from Diamond City onto target creature. Activate only if two or more creatures entered the battlefield under your control this turn.

A creature with a shield counter on it may still be destroyed by state-based actions if it has damage marked on it equal to its toughness or has been dealt unpreventable damage by a source with deathtouch.

If a permanent that would be dealt damage has more than one shield counter on it, that damage is prevented and only one shield counter is removed.

If a permanent with a shield counter is dealt unpreventable damage, that damage will be dealt and a shield counter will still be removed.

Removing a shield counter when a permanent would be dealt damage or destroyed isn’t the same as regenerating a permanent.

Shield counters don’t prevent players from sacrificing permanents.

“Shield” is not an ability that permanents have and shield counters are not keyword counters. If a permanent with a shield counter loses its abilities, the shield counter will still protect it as normal.