Live demo app: http://runnable.com/VGJozZBtZw5RAg7d/forem-with-desc-replies
views/forem/topics/show.html.erb
<%= render partial: "forem/posts/post", collection: topic.desc_posts, locals: { topic: @topic } %>
decorators/models/forem/topic_decorator.erb
Forem::Topic.class_eval do
def desc_posts
posts.order("forem_posts.created_at DESC")
end
end