The Squid Girl is the Tanid way of taking advantage of water tiles. Her starting speed is practically unmatched on water and slime, and it lets her position herself to use her skills to their full positional advantage.
MagicPull is an incredibly powerful skill that allows you deal with priority targets before the enemy even has a chance to engage. It's a range 6 Grab, that also adds an attack that scales with both strength and magic. It's a very flexible tool that allows you to set up isolated targets for yourself or your teammates. It's an inheritable skill that can shine on many other units.
InkSpurt is a free reposition tool, that allows you to blind your enemies, while also creating slime zones for your team.
Sadly her advantages end when she's outside of water. Her aquatic trait doesn't work on slime, and her movement outside water/slime is just pitiful. It doesn't help that she doesn't naturally learn spells to support her great magic growths either. Her only passive, a Blind(-Armor, -Speed) on being attacked, doesn't see much use when her extremely low hp growths force her to stay away.