Freeze a springform pan (or 6" cake ring if you're going for the Momofuku style layered cake) for at least 30 minutes.
Pulse one package of Chocolate Wafers at a time in a food processor until they're coarse crumbs (you don't want them to be too fine or they'll clump together).
Pour the crumbs into a medium bowl and add in both bottles of Magic Shell chocolate sauce - mix well, set aside.
Mix the cold water and gelatin in a microwave safe dish. Allow to sit for 1 minute, then microwave the gelatin for 30 seconds to make it liquid again. This will stabilize the whipped cream.
Using a whisk attachment, mix the heavy cream on medium speed and gradually increase the speed to high. Once it starts to thicken, add in the confectioners sugar and liquid gelatin. Once stiff peaks form, add in the vanilla and whip until it's well incorporated - set aside.
Once the pan is cold enough, place a layer of chocolate ice cream down. If using a springform pan, use enough ice cream to make it halfway up the pan. If using the Momofuku method, line your cake ring with a strip of acetate and place this on a cardboard round; then spread an even layer of chocolate ice cream. Place an even layer of crunchies on top of the ice cream and place in the freezer for 10-15 minutes.
Next, add a layer of vanilla ice cream. Repeat the process again if using the Momofuku method (adding strips of acetate as you build upward), until you've reached your desired height. Be sure to make the top layer of the cake as smooth and even as possible. Once layering is complete, place the cake in the freezer for at least a few hours or overnight.
Remove the cake from the freezer and carefully remove the springform pan or cake ring (you may need to run a hot washcloth around the edge to loosen it from the pan). Carefully remove the pan or ring.
Decorate the cake with the stabilized whipped cream and additional crunchies as desired.
Place the cake back in the freezer to set and be sure to remove it 10-15 minutes before serving to allow it to thaw.