You can view risk mitigation efforts for any individual using the risk matrix. To view risk mitigation for an individual risk, you must have multiple baselines with various mitigation efforts for this risk.
Mitigation efforts for the risk can entail:
•  Reducing the chance of occurrence or outcome of the risk
•  Changing the outcome
•  Changing the mutually exclusive alternatives associated with the risk
•  Changing the project schedule, e.g. executing a number of additional activities on the specific baseline
•  All the above

Mitigation efforts for a specific risk are shown as a “waterfall diagram”.

See also

Analyzing Risk Mitigation Efforts with Multiple Baselines

Comparing pre and post-mitigation baselines