Hatchery Sliver + Crimson Kobolds + Leyline of Transformation

Hatchery Sliver

Crimson Kobolds

Leyline of Transformation

How it works

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