Hangarback Walker plays well with Hardened Scales... but casting Walker for 0 isn't going to work out well for you.
Tag: Hangarback Walker
Hangarback Manifesto (a manifested Walker is not very good)
Turning a manifested Hangarback Walker face up doesn't put counters on it (you can't even pay mana for X), so it will generally die immediately after it turns face up, before you even get a chance to activate its ability.
Hangarback Walker vs. Eidolon of the Great Revel and Disdainful Stroke
The X's in a spells cost are counted as having the value chosen for it while that spell is on the stack. As such, Hangarback Walker for X=1 means a CMC of 1+1=2, and it would trigger Eidolon, while X=2 means CMC 2+2=4 to evade Eidolon's trigger.