In a small saucepan, melt the chocolate with 1/2 cup cream over medium-low heat, stirring until smooth. Let cool.
Meanwhile, using an electric mixer with a whisk attachment, whip 2 cups cream with 1 teaspoon vanilla until stiff but not dry.
In a medium bowl, whisk together the pumpkin and marshmallow cream. Fold in the whipped cream in 2 parts; refrigerate. Add the remaining 1 1/2 cups heavy cream to the mixer bowl and whip until thickened. With the machine on, slowly add the chocolate mixture and the remaining 1 teaspoon vanilla and beat until stiff but not dry.
Spread one-third of the chocolate cream in a 4-quart clear glass trifle bowl. Layer with one-third of the toffee. Stand 8 cookies on their edges around the perimeter of the bowl. Make 1 stack of 4 more cookies sandwiched with some pumpkin cream, topping with more cream. Repeat with the remaining cookies and more pumpkin cream to make a total of 14 cookie stacks Place 7 stacks in the trifle bowl. Top with the remaining pumpkin cream and half of the chocolate cream. Sprinkle with another third of the toffee. Top with the remaining 7 cookie stacks and chocolate cream. Cover and refrigerate for at least 6 hours and up to 24 hours. To serve, sprinkle with the remaining toffee.
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