Finally, the deck aims to put tons of cards into your graveyard, and then take advantage of this (for example with Izoni, Thousand-Eyed, Golgari Grave-Troll, Jarad, Golgari Litch Lord, etc)
Frankly, these two cards are roughly equivalent
I mean Stuffy and Mindcrank is pretty easy all around
This can be activated for 0 to destroy a Reflection, so if someone has a Reflection token that would stop your creation just randomly, like the Changeling made by Crib Swap, you can destroy it to make your 2/2
Motunui Island Paradise Motunui is an incredibly effective location and you can actually get it in the Ruby/Sapphire starter deck (although its cheaper online via the link above)
Considering that Arachnogenesis is from Commander 2015 , which means it's nearly a decade old and has never been reprinted, a large part of its current price is due to its low supply