In a deck built around fungi, Pallid Mycoderm buffs your board better for just one more mana, so I wouldnt bother with this one unless youre reaching for filler
Mana ramp cards like Sol Ring or Coldsteel Heart also help to determine the number of lands you can play, since these ramp spells let you hit the determined spot of mana where your deck operates the best
Whats great is that upkeep trigger: sacrifice another creature for a +1/+1 counter on the Gutter-Dweller is sweet, but of course the real juice is the impulse draw, like an Outpost Siege trigger
Whenever you cast a noncreature spell, put a +1/+1 counter on Vivi Ornitier and it deals 1 damage to each opponent
Still it's a solid shadow beater, and you can generally depend on it connecting and generating combat damage triggers which is pretty worthwhile
Every aspect of this feels a bitforced