EntranceThemeTransition code only

transition.cs

// Create an instance of EntranceThemeTransition
EntranceThemeTransition entranceThemeTransition = new EntranceThemeTransition();

// Set the properties of the transition
entranceThemeTransition.FromHorizontalOffset = 100; // From where the animation will start horizontally
entranceThemeTransition.FromVerticalOffset = 100; // From where the animation will start vertically

// Get the parent container of the element
var panel = myElement.Parent as Panel;

// If the parent is a Panel and doesn't already have transition set, 
// then apply the EntranceThemeTransition to its ChildrenTransitions collection
if (panel != null)
{
    if (panel.ChildrenTransitions == null)
    {
        panel.ChildrenTransitions = new TransitionCollection();
    }

    // Add the entranceThemeTransition to the panel's ChildrenTransitions
    panel.ChildrenTransitions.Add(entranceThemeTransition);
}

// Now when you change the visibility of the element from Collapsed to Visible, 
// it should animate in with the EntranceThemeTransition
myElement.Visibility = Visibility.Visible;