I feel like I should know this by know, but animation scripting in Unity has always given me grief in the past.
Let’s say I’ve got a first person weapon. The weapon has an Idle animation, a Fire animation, and a Walk animation.
Playing these individually, one at a time, is no trouble. However, if I’m walking (the Walk animation is playing) and then start firing (the Fire animation is playing) it looks wrong when the Walk animation is suddenly stopped.
However, I’m breaking my brain trying to figure out how best to blend the Fire animation with the Walk animation. I could make Walk procedural, but I think it would afford a lot more artist control to have it as an animation. Playing Fire as additive also tends to wreck my animations (it never returns to rest, so the hands just push away forever).
Any ideas?
Well 'oly crap. I just solved it.
Turns out my base “idle” animation was completely still. Therefore, I didn’t notice that it stopped playing when the “equip” animation played. 
The way I found this out was by swapping out my idle animation for the reload animation (so it constantly reloads while idle). But it didn’t reload… until I set everything but the idle animation to layer 2.
Once I got that working, having my fire animation set to “additive” seems to work perfectly fine now. Guess it just needed a base animation to add to.
what about animation.CrossFade()
Not what I’m asking for. That still makes the walk animation stop (just over time instead of immediately), and the fire animation loses all “punch” if you know what I mean (and if it’s quick enough, might not even look like it’s playing).