Defend

Defend, also known as Guard (Japanese:  Guard) is a battle command appearing in all three games in the Mother series.

In
In Mother, the Guard command halves all damage from both physical- and PSI-based attacks, at the expense of not moving for that turn. The effect stacks with PSI Shield and defensive equipment. All playable characters and some enemy characters can use the Guard command.

In EarthBound
In EarthBound, the Defend command halves only physical damage, and even then, some physical attacks are unaffected. However, it has a new usage: guarding slows the scrolling HP meter until the turn is over. All playable characters and some enemy characters can use the Defend command. Ranged weapons, such as yo-yos and slingshots, bottle rockets, and other explosives are unaffected by this command.

In Mother 3
The Defend command remains relatively unchanged from EarthBound.