Hatchery Sliver + Phyrexian Walker + Leyline of Transformation

Hatchery Sliver

Phyrexian Walker

Leyline of Transformation

How it works

1. Cast Phyrexian Walker by paying 0, and choosing to pay its replicate cost an arbitrarily large number of times by paying 0.
2. Phyrexian Walker triggers, creating a copy of it for each time its replicate cost was paid.
3. Resolve all Phyrexian Walker spells, causing the nontoken Phyrexian Walker to enter the battlefield, and creating a token copy of it for each time its replicate cost was paid.

By starting the game with Leyline of Transformation already on the battlefield and declaring Sliver as the chosen creature type, every creature you control, own, and cast becomes a Sliver in addition to its other types. This grants your creature spells the innate ability of Hatchery Sliver, allowing you to pay an extra {1}{G} for each time you wish to replicate a creature spell. However, because you are casting Phyrexian Walker for its mana cost of {0}, its replicate cost conveniently evaluates to {0} as well. This lets you flood the battlefield with an arbitrary number of token copies alongside the original creature for absolutely zero mana.