When Nethroi mutates, you get to bring back any number of creature cards with a total power of ten or less to the battlefield
As with any repeatable utility land it is on the expensive side to use and will thus be a fairly minor boost to synergies most of the time
In particular I love it in combination with Slaughters buyback life loss
Cantrips like Opt and Consider are essential: they give me cheap card selection and the ability to dig for answers, and when paired with value engines like Talrand, Sky Summoner and Murmuring Mystic, they can add up to a massive board before long
The 1996 World Champion card summons a creature with a power and toughness equal to the opponent's remaining life
Even though it is Indestructible, it still takes damage, consequently triggering its ability, so it is interesting to use these cards to keep it on the board for as long as possible