In terms of criteria here, well look more favorably on precons with a cohesive, consistent game plan, and a well-defined strategy that feeds into what the face Commander does
How this happens varies wildly
The original spell will be on the stack beneath those copies and will resolve last
Unholy Annex // Ritual Chamber Unholy Annex // Ritual Chamber starts off with a slightly worse Phyrexian Arena considering the amount of life you pay, but this room enchantment is more complete
Sometimes the damage is what initiates the combo, which is always interesting - Polyraptor is a common way to turn the card Pyrohemia into a value minting machine, for example
These 15 picks include some of the top MTG cards for removal, recursion, and raw efficiency the kind of spells that swing games the moment they resolve