[@Wraithblade6]

Lightsabers are able to cut through most anything, but Magnus IS stupidly tough. A lightsaber would be able to cut him, but slowly, and with great effort. It would have to be continually applied and 'pushed through' over the course of several seconds. Similar to attempting to cut a block of mandalorian iron.

Of course, certain Sith and Jedi are able to enhance the power of their Lightsabre, at which point it becomes dependent on the Sith/Jedi in question. For example, a full-power Luke Skywalker could probably slice through Magnus like butter, being the most powerful Jedi in history, assuming we take Legends!Luke.