Imperfected
Member
You've got to stay in on him.
You're probably only going to get one swing off with most weapons before having to dodge again. You might want to use a quicker swing state of whatever weapon you are using, even, because the recovery on some meatier weapons might be too long to get a safe swing.
You're going to eat his jump-back kusari-bullshit ground-raker thing. Yes, it's possible to dodge consistently, but only if you're leaving so much potential damage on the table that it ceases to be worth it holding back swings just to be able to anticipate it. Unless your stats are super weird, it shouldn't be fatal, so whatever. Cost of doing business.
He has a really nasty follow-up charge attack that has a tendency to get hidden by the clouds of smoke he kicks up by the attack it follows from. There's not much of a good tell on it as a result. Assume he's always going to do it if you're too far away from him when he whiffs one of his big vertical swings.
You can't really do much to stop him from just jumping around fanning out grenades like some kind of moronic ninja jackass. My advice is to start playing another game when he goes into it, maybe Pokemon or something, and kind of half-remember to dodge or vial back up now and then until he's done throwing a tantrum and wants to be interactive again.
The big attacks you need to learn are: the Lightning Storm Scream thing (as another poster here clued me in, the beached whale is where the storm starts from, and there's a tiny little gap in the wave of lightning you can run through; yes, they expected you to completely swing your camera away from the boss during the middle of the fight because of your psychic intuition that a whale carcass was sending rolling thunder at you, and PS, make sure you aren't standing anywhere near the goddamn thing during his second phase, ever), the follow-up swings to his sweeping attacks that are pretty specifically designed to catch you trying to get back out of range to heal (probably better to man up and heal right in his face; call him a punk-ass bitch while you do it), and just sort of be aware of the fact that like half the other bosses in this DLC he has an OTG that does massive damage. (So, uh... don't get knocked down, I guess? There doesn't seem to be a quick recovery system in place if you get truly flattened...)
You can also parry him. Almost everything he does can be parried in his initial state. I'm not sure about his secondary form; a lot of those attacks either can't be parried, or the distinction is largely academic anyway because he's never going to use them when you're in a position to reasonably do so. His melee can still be parried, but when he's in melee mode that's also your best time to go aggressive, so it might not be that useful...
