Features used to implement the example

Example: Make a custom field mandatory when priority is "Critical" or "Blocker" and issue type is "Incident"

We will be able to implement this requirement using Boolean validator with math, date-time or text-string terms. I have implemented it successfully in a beta version of the plugin using the following configuration:

Text to be parsd is: %{00014} != "incident" OR (%{00017} != "Critical" AND %{00017} != "Blocker") OR %{10700} != null

Or to implement it we can use validator Validaton based on regular expression with the configuration shown in the following screenshot:

Text to be parsed is:

%{00014}@%{00017}@%{10700}

Incidnet@(Bloquer|Critical)@

Note that:

To evaluate the value of fields Priority (field code %{00017}) and Consequence of bug (field code %{10700}) at the same time we compose a text with both fields using character '@' as separator.
We check "Negate validation" since the regular expression introduced describes the kind of input we don't to admit.