Hello Horst,

I have been looking into your question and after research I determined two things:

1. Thickness property is not available for Markers. This means that only the “Opacity” can be changed.
2. To access the markers of the series and apply custom animation, you have to get all series  markers and loop through the entire collection in order to define the one, which  IsMouseOver property is set to true. It will happen every time when the mouse hover or leave a marker so it will invoke a huge amount of iterations and will cost an issues with the performance and even possible unexpected behavior.

A better and more performant way for achieving your requirement is to use style trigger for the Marker. In this style, after checking if IsMouseOver property is true, the Opacity could be set to the desired value.

  <Style x:Key="test" TargetType="{x:Type ig:Marker}">               
                <Style.Triggers>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter Property="Opacity" Value="0.5"/>                        
                    </Trigger>
                </Style.Triggers>
            </Style>

I modified the previously attached sample according to this suggestion. I am keeping the animation for hovering the item through the legend.

Please test it on your side and let me know if I may be of any further assistance.

Sincerely,
Teodosia Hristodorova
Associate Software Developer