What both of the people above me said, though I think KDJ has solo'd locals with Zelda despite not using Dins.
All of the uses old din had you can still do with new din, and then some. Before it was a ****ty move that only ever worked if you outthought your opponent really hard (which is impossible to do against good players who have ever played against Zelda). It was a channel, and a long one at that since it moved so slowly, had a small hitbox that, when coupled with it moving so slowly, meant it only covered a specific area at any one moment, and put you into freefall if you used it midair (so you really couldnt). Think of it like if you could only fire off one of Mario's fireballs at a time but also couldnt move or use other moves as long as it was out. It blew.
New PM din lets you set up mines, temporarily controlling space for an extended, non-channeled period of time (past the initial channel). After 3 seconds the mines all explode, doing what old din used to do but relinquishing control of the space. The fuses are extended an extra 3 seconds every time you set a new din, but only 3 can be active at once. Transforming also explodes the mines. Oh and no freefall.
Setting up mines like in the Zhime video Kaeldiar linked will allow your friend to punish people with other moves during their hitstun. Zhime also times the explosions sometimes, which is another tactic. This is a creative, strategic, and dynamic playstyle. Results may vary.
If your friend wants to do the same thing he did before with Zelda, he can do almost exactly the same thing (but with more control) by placing the mine directly on the opponent. This will do pretty much the same thing it did in Melee, with the added benefit of continuing to offer that hitbox for 3 seconds.
