The extras don't say but it's implied that the murials are of San Lang's wishes for being with DianXia, the extras only focus on the statues not the murials.
Hualian Supremacy! Their love will last a billion years
I'm not so sure but imo I think it's about the mural with the scene of Xie Lian being flustered and kinda half naked after being hit with the aphrodisiac from those flower demons back when he descended to help his people ╮(￣▽￣)╭
Or the fact that one of The Land of Tender shapeshifted into a naked DianXia, which is why a young San Lang got so mad.
I love mdzs and i thought that there's no other story that as good as it but when i read this and finished the novel shit this is really really good hua cheng's unconditional love for xie lian can't compare to others....and the scene where xie lian freed hua cheng's soul from the lantern and their conversation there makes me cry whenever i remember that.
By the way what did feng xin and mu qing see in mt tong lu that they don't want xie lian to see? I haven't read the extra yet...