Well, I want to get the second secret ending and that's why I have to complete the whole journal, I'm only missing the Organization Data fights and Lingering Will. Any advice to defeat them all without any difficulties? I'm playing at Proud, I have the Ultima Weapon and Fenrir, my stats as far as I remember are:
Attack: 70
Magic: 65
Defense: 72
I'm planning to increase those to 80 both Attack and defense and 75 Magic.
It'd be a lot easier if you stock boosts items for Sora. Only Defense Boosts and Strength Boosts. It can take you a week or less to get synthesize items ready. The Lingering Will be the your only struggle once your stats are over 100. I have mine on 125/135 and it was a nightmare the moment he started to negate my commands whether magic or attack. My magic is weak, so when he negates my attack. I remember just flying around until he it turns off again but he usually throws his giant beams balls than you can guard back against him to damage him on that current shield he's on. And whenever he negates the magic command. He's usually trying to chase you down but go onto your drive and use limit for him to flinch and when he does. Attack him down until his actual health appears and keep attacking him until he tries to negate one of your commands again like that that's how you bring him down until the end.
As for the Data Battles. You can set your stats ready for the Lingering Will and they'll be a lot easier for you or you can fight them exactly how your stats currently are but you have to recognize the strategies for each battle. Meanwhile, if your stats are over 100 then you don't have to rely too much about dying and just recognize the same strategies it takes to take them down.
Xemnas: You got to be careful when he's starts hitting you with the sabers; he gets you stuck on that for 20 seconds.
Xigbar: Got to be quick on attacking him but you can guard against his attacks to reflect them back.
Xaldin: You got to keep using the Jump reaction command.
Axel: The entire floor will go on flames bringing your HP down little by little. You can keep attacking him but you'll need to clear the floor in order to really kill Axel. He's usually goes off the arena and you'll need to trigger the reaction command quickly in order to clear the floor.
Luxord: You can take him down until there's a moment when you have to gamble with him and finish him off.
Saix: He's goes berserk. The moment his berserk level goes down that's when you need to strike but for you to do that. You have to pick up his weapon and use it against him and then hit him with all you got with the keyblade.
Larxene, Laxeaus, Vexen, Marluxia & Zexion: Exactly how it was for the Absent Silhouette.
Demyx: Get your wisdom form ready. You'll need to burn over different sets of water Demyx under 30 seconds each. He's goes from 13, then 25, 50 and 75. Just fight him through until he does it again. The sets for the second time, 13, 25, 50 and then 99. You have to go through the second set to kill him off.
Roxas: Exact same way how you battled him on the Deep Dive.