i was trying to kill my opponent by dragging his non-aquatic dudes into the water using the magnetite beacon, he just kept walking them out of the water though.

I don't know if this is a bug, but i felt they should have drowned. Also, dragging aquatic units onto land should take away their ability to move.

The Beacons move affect doesn't dim the unit.
To really use the Beacon effectively you have to wait until he's moved his units, that way they're dimmed and can't move.