Nevan is one trouble....
Target : Nevan
Obstruction : Nevan Bat Barrier
Style : Doesn't matter
Equipment : Rebellion & Doesn't matter
Gun : Twin Gun & Spiral
Breaking Barrier :
She will start striking you with her bats,it's slow,so just roll around,Stinger to her sometime,when she cast lightning pillar,it is advised NOT to get near her because she will cast some nasty bats to you (3 hits).However,if you are quick enough,Stinger another time.
Repeat the process until her shield is broken.Then Full ofence + Devil Trigger.She'll be vulnarable for 5 sec.
Once Nevan's HP decreases by half,she'll cast Shockwave,you can easily notice by the ground's colour changing,Jump then riddle her with your basic gun.She'll then cast that Pillar or some sort,evade and use Spiral sometime.
Neva's last set of move,is the easiet,you dont actually have to brake her shield.She'll break it for you and come to you,beware,jump and riddle her with your basic guns first before executing Helm Breaker with large pack of combos.
You wont have trouble with that.
2 Sets I didn't mention...Bat Sphere and Bat's Drive
bat's Sphere will deal you a nasty damage if you recieve a continual damage.However,she is very vulnarable after that.Easily notice when she runs directly to you.
Bat's Drives : Nevan cast's a black Spike toward you nasty damages...Jump toward Nevan above the Spikes and show your prowess.
To GTX : My advise on Leviathan
Target : Leviathan's Heart...
What you need to do is hit either left or right organ until their life bars depletes then the heart will open...
I strongly suggest offensive on the left organ,blue one which has lower defend...just keep jump + helm breaker until it's done,the heart should execute a cleaner laser which benefits you..Jump while shooting it with your Normal Gun...Once the ray are gone,Devil Trigger + Full Offense on it,dont bother about style really...