Hello
Hydra cannot pass an object from Delphi to .NET or vice versa. After all what would do a Delphi code with a received instance of System.Data.DataTable? It knows nothing about methods and properties it does expose, so it wouldn’t be able to call or access them.
Instead Hydra passes interfaces, not objects. A plugin defines a set of interfaces and then these interfaces are imported into the host app project. Then an object can be created on (f.e.) .NET side and then a pointer to its interface is being passed to a Delphi app. Then Delphi app can work with this object - it can call its methods and properties.
This topic contains a short tutorial how to do this and sample projects: Need a Jumpstart with Delphi XE3 and .NET 2.0 DLL Assemblies Integration
Hope that helps