I was initially playing it in the sideboard over Elder Gargaroth but I wanted to give the 6/6 Beast a try as the five-mana threat in sideboard games that needs to be answered ASAP. The biggest problem I found with Vivien is that, much like Garruk, a 3/3 isnt that impressive and given that it only goes up to four loyalty after its first activation (unlike the absurd six loyalty that Nissa, Who Shakes the World went to), its just not that durable
Acidic Slime Commander: Kamigawa: Neon Dynasty | Uncommon In EDH, you need diverse tools that are set up to deal with any and every situation
Spidersilk Net
Otters weren't powerful enough and thus didn't see constructed play
I suppose you could Teleportation Circle it over and over to tutor planeswalkers to your hand, giving it some utility in your Djeru, With Eyes Open or Cadric, Soul Kindler decks, though Id have to question at that point why you wouldnt just blink something like Thalias Lancers or Djeru himself
This can quickly grow Vogar into a serious threat thats hard to block due to menace