Two y-axes
Plot values with different units together. Bind each axis to a serie with seriesName and move the second one to the right with opposite.
Threshold line
Draw a target or a limit across the plot with annotations.yaxis, so a reader sees at a glance which points miss it.
Marker lines
Mark the moment something happened with annotations.xaxis — a release, a campaign, an incident.
Brush and zoom
The small chart below picks the range shown above. Point it at the main chart id with chart.brush and render the main chart first.
Synced charts
Charts that share a chart.group name follow one another — hover or zoom on one and the rest do the same.