Creating a living fey siege engine

I've been trying to wrap my head around whether this is possible.

I'm currently creating afey species that's mainly rooted (ha) in the earth path.

What I want is to have a somewhat large earth elemental (doesn't neéd to have the elemental ability in this case) to chuck some explosive projectile to the enemy (fluffed as throwing his little explosive clay buddies overhead towards the enemy).

I initially thought about making it a siege engine, but realized that that isn't a living thing and is stationary (unless crewed). I also don't see how I couldhave easy access to that without using forbidden knowledge, which'll get quite pricey quite fast I suspect.

Alternatively, I thought to create an incarnate class for earth, and I wanted to give it flaming fist power from fire, but that's not allowed of course. Next, I thought about creating a primal-based incarnate class, give it the Monster 2 ability from an incarnate 2 trait in order to give it an internal monster power. But that may be rendered unusable because the incarnate class says it -only- allows traits and such from the chosen path.

Does anyone have an idea as to how I could do this (preferably without simply using a fire-based class, because it'd clash with the theme)?

Thanks in advance!

Edit: forgot to mention I'd like this to be a lv1 or lv2 class.