In these matchups, we can swap them out for some big, resilient, hard-to-interact-with threats
Mauhur helps grow this army even larger, and a number of cards synergize with the army including Ugluk (grows when the army or any other creatures die), Gothmog (grants the army deathtouch), Moria Marauder (play spells off the top), Sauron (ring tempts, card draw)
One issue I've run into as an avid sacrifice gamer in different formats is that you can get an engine going and accrue value slowly without ever actually slamming the door shut on a game
It doesnt matter that Moss Viper only has one power
All it does is make a card colorless regardless of the colors that appear in its mana cost, but it should have no real bearing on your decision-making process
Just shuffle it away