Hatchery Sliver + Ornithopter + Leyline of Transformation

Hatchery Sliver

Ornithopter

Leyline of Transformation

How it works

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