Year over year Variance - based on the example below - Very Hard

For scenario-based YoY variance (not just calendar year), the standard DATEADD won't work, you need to define your scenarios as a separate dimension and use CALCULATE with explicit filters.

Basic pattern:

YoY Variance =
VAR _curr = CALCULATE([Sales], Scenario[Name] = "Current Year")
VAR _prev = CALCULATE([Sales], Scenario[Name] = "Previous Year")
RETURN DIVIDE(_curr - _prev, ABS(_prev))

If the complexity keeps growing (multiple scenarios, multiple metrics), it's worth looking at Flexa Tables on AppSource, YoY and scenario comparison are built-in buttons, no DAX required. Users switch scenarios themselves in the published report.