It can attack and block, even if another creature is carrying it
With a Stranger Things vibe and some genuinely unsettling art, Duskmourn is looking to tap into a niche that the MTG universe has rarely investigated directly, choosing to include hints of horror (like Eldrazi transformations) or more traditional fantasy scares (think Innistrad - before the Eldrazi, anyways)
Best in the land ramping decks as it kills less of your own stuff
If you use Expansion to copy Reverberate, for example, that copy can target Reverberate again, creating a loop of copies
Its an endure X ability, where the X is determined by the number of counters on Warden of the Grove
Two tera SIRs for eevee in same set is so unnecessary