Can Minespine attack from underground?

Underground, Minespine keeps fighting: the burrow is a position it attacks and casts from, not a pause to wait out. While it stays down, ordinary enemy attacks have nothing to target. Only attacks built to unearth a burrowed Aniimo can reach it.

That fits what Minespine is for. It is an Earth-element Aniimo with a breaker role, so the burrow lets it keep up pressure while most of what the enemy throws back misses. The catch is the unearthing attacks. Against an opponent that has them, the burrow stops protecting Minespine, so look at what you are fighting before you rely on it.

Combat runs in real time, and your Pathfinder fights alongside your Aniimo with attacks and gadgets. That means you are still in the fight while Minespine is underground. The linked Earth and Grass combat article explains burrowing in full.