The List

Hangarback Walker

Hangarback Walker enters with X +1/+1 counters on it.
When Hangarback Walker dies, create a 1/1 colorless Thopter artifact creature token with flying for each +1/+1 counter on Hangarback Walker.
{1}, {T}: Put a +1/+1 counter on Hangarback Walker.

Commander Masters

Hangarback Walker enters the battlefield with X +1/+1 counters on it.
When Hangarback Walker dies, create a 1/1 colorless Thopter artifact creature token with flying for each +1/+1 counter on Hangarback Walker.
{1}, {T}: Put a +1/+1 counter on Hangarback Walker.

Jumpstart 2022

Explorer Anthology 1

Love Your LGS 2020

Kaladesh Inventions

Magic Origins

Hangarback Walker enters the battlefield with X +1/+1 counters on it.
When Hangarback Walker dies, put a 1/1 colorless Thopter artifact creature token with flying onto the battlefield for each +1/+1 counter on Hangarback Walker.{1}, {T}: Put a +1/+1 counter on Hangarback Walker.