Crawl is good for being able to move under projectiles. Most characters can't hit low enough to peg a crawling Snake, expect for Pit 'cus he's rigged. Pit can arc his to hit a crouching Snake, but nobody else can lower the height of their attacks like in Melee. If you try to short hop a laser or something, they just finish the animation on the ground, at standing height, instead of shooting it really low like before. Crawling gets you close and you can do down-tilts really fast from it.
Mines would be good for edge-guarding if everyone didn't auto-sweetspot. If you lay one on the edge, they just jump over no problem. Also, the downsmash mines can hit Snake just as easily as they can hit the other guy, so I tend to stick with the down-B version. It seemed like a cool mechanic, but in the end a downsmash mine just turns into a prox mine item. It's not really useful to lay it since either of you could hit it.