When Survey Mechan dies, Mortuary triggers, putting Survey Mechan from your graveyard onto the top of your library.
Teval triggers, creating two creature tokens.
Resolve the Survey Mechan ability, dealing 3 damage to any target and causing you to draw three cards and gain 3 life.
Activate Ashnod's Altar twice by sacrificing the two creature tokens, adding CCCC.
Cast Survey Mechan by paying 4.
Repeat.
This intricate engine turns Survey Mechan into an endlessly looping projectile, fueled entirely by the card-manipulating magic of Mortuary and the mana-generating sacrifice outlet of Ashnod's Altar. As Survey Mechan goes to the graveyard and triggers Mortuary to place itself right back on top of your library, Teval, the Balanced Scale brilliantly exploits those cards leaving the graveyard to continuously spawn Zombie Druid tokens. Those tokens are instantly doubled by Chatterfang, Squirrel General's replacement effect, providing more than enough sacrifices for Ashnod's Altar to fund the Mechan's repeated casts and activations.