This enemy has extremely powerful long-distance area attacks. At 100% strength magnification, it does 54,000 damage, so not many non-Ubers can survive a hit from it. Fortunately, Hackey has a very large blindspot, even larger than that of the original Tackey, only hitting between 1,200~1,500 range, so it's easy for fast-moving units like Awakened Bahamut and Sanada Yukimura to get in.
Try to get your fast moving units past the blindspot and take out this burning seahorse, but beware... If Hackey lands a hit on your units they'll be toast!
Overall, much of the same strategies that work against the original Tackey should also work against this enemy, but you do not want it getting a hit off on any of your important units.