[quote=@Cu Chulainn]Grants Lancer a rank-up to all parameters while in enemy territory.[/quote]
This is probably the most fitting ability that I can think of for this type of HGW in the right circumstances. 
One issue I can find is that the Riding skill should probably be ranked-down similar to Arturia when summoned in Saber class, since it seems class skills outside of your own incurs a penalty normally (with some exceptions).