Running json_encode on the vars list treats it as a non-associated list and encodes it as an array, not grabbing the contents of the variables to encode as an object.
[13:57:13] <%MrStonedOne> !dm var/mob/m = new();;json_encode(m.vars)
[13:57:15] <+Bot32> TheAlmightyStoner: ["type","parent_type","tag","name","desc","suffix","text","icon","icon_state","overlays","underlays","dir","visibility","luminosity","opacity","density","layer","gender","mouse_over_pointer","mouse_drag_pointer","mouse_drop_pointer","mouse_drop_zone","verbs","vars","contents","invisibility","infra_luminosity","pixel_x","pixel_y","mouse_opacity","pixel_z","override","maptext","maptext_width","maptext_he...
(the final command is wrapped in a world.log << "[]")