Typically, most buffs are generally 40% this mostly comes from ninjas that use an Auto Barrier at the start of the battle.

This is also the same with most Barrier Ninjas as their mysteries (Such as Sasuke and Gaara).

Then you also have buffs that happen at the start of the battle that will increase by 30% Such as Iruka and Guy. However these last only for 3 rounds.

Then you have your Main Character's talent that uses some kind of enhancement that boosts ninjutsu and attack by 40% for 5 rounds.

Different ninja give different buffs. I'll list the ones I remember off the top of my head here.

Note-Buffs can be removed by Han, or someone of the sort, and barriers can be overwritten, so as long as your barrier is in effect, you have the buff. If a ninja isn't listed with a specified attribute, it means both Nin and Attack get the buff.

Auto-Barrier buffers. (These guys make a barrier at the start of the game, lasts 3 rounds) These all give attack and ninjutsu buffs.

Darui-40% to all Lightning and Water Ninja.

Haku [Edo Tensei]-40% to Wind and Water Ninja.

Mei Terumi-40% to Water and Fire Ninja.

Onoki-40% to Wind, Earth, and Fire Ninja.

Danzo-40% to Lightning and Fire Ninja.

Gaara(5th Kazekage)-40% to Wind and Earth Ninja.

Shisui-40% to Lightning, Fire, and Wind Ninja.

Normal Barrier Ninja (Barrier is Mystery)

3* Gaara-40% to Wind Ninja.

3* Sasuke-40% to Lightning Ninja.

Yamato-40% to Earth Ninja.

Jirobo-40% to Earth Ninja.

Haku-40% to Water Ninja.

Anko-40% to Fire Ninja

Hashirama (1st Hokage)-40% to Konoha/Leaf Ninja.

Note-Roshi, Tendo make barriers that have no buffs, Itachi's barrier is only a chakra machine, and shark Kisame's is a mass control one.

Normal buffs-Added on, eventually expire after X number of rounds and can be removed via Han, gnw Temari, or others.

Guy-30% Taijutsu buff to your entire team. (your team only), 3 rounds.

Sasori [Edo Tensei]-30% to 9 Edo Units for 3 rounds.

Mifune-30% to 9 sword users for 5 rounds.

Konan-30% to 9 (Or all, I don't remember) Akatsuki ninja, 3 rounds.

Hashirama Senju (1st Hokage)-30% Nin Buff to your entire side (all 3 teams) for 5 rounds, permanent buff in skillbroken.

Tobirama Senju (2nd Hokage)-30% Tai buff to your entire side (all 3 teams) for 5 rounds, permanent buff if skillbroken.

Jugo-30% to curse mark people, lasts 3 rounds.

Pain-Chikushodo-40% Nin to all Rinnegan units.

Pain-Shurado-40% Tai to all Rinnegan units.

Toroi-20% to any Lightning ninja with a shield.

Killer Bee (7 Sworded Thug)-30% to Jinchuriki, 3 rounds.

Samui-30% to Cloud Ninja, 3 rounds.

Hebihime(Agate)-30%(?) to all...yeah, I don't remember, sorry, but hey, it's Hebihime, she's not even real.

Iruka-30% to Leaf Ninja, lasts 3 rounds

PB Sasuke-30% to up to 9 female ninja, lasts 3 rounds

Then we have people who apply their buffs, but don't expire or are removable by Han.Includes Scaling buffs.

Both Edo Asuma and WB Asuma-30% I think for WB, but for sure Edo for any nin at full hp.

Skillbroken Senju bros, see their listing regarding skillbreaks in the above section.

Kisame, 3rd Ay, others, I don't wanna find them this late at night-X chakra gives X attack and X ninjutsu, varies, I'll get a full list later.

Roshi-gets more Nin (and Defense) every time he's hit by a taijutsu attack

Kage Minato-9% Tai each time he actives flying raijin slash.

Sailor Sakura-gets more attack each time she gets hit.

Jonin Minato-+9% Tai each time he activates his chase.

Edo Yagura, Unreleased-13% everytime he activates his chase...he's sorta broken looking.

2* Sasuke-I think he gives +nin per times hit, low though.

Tayuya-+nin each time hit, probably low

Ukon and Sakon-+tai each time hit, probs low

Deidara-Each time he causes ninjutsu damage, increase damage dealt by 4%

Ameyuri Ringo-12% per lightning nin

Jinin Akebino-60% per skill point, up to 240%....jeez

DW Hinata-13% per female unit

Madara-20% to Konoha Nin

Thanks to MuroiMaNin for the Madara ordeal

I'm not writing anymore until 2018...happy new years (This was written 12/31/2017, 11:37PM)

Only includes offensive buffs, and no buffs like Resistance rinnegan, shields, combo rate from Kinkaku, etc.

madaras buff isnt removable but he still *s and i am 99.99999% sure that asumas buff is 30/30 not 40/40

Ah, okay, sorry, wrote that pretty late at night.

~ I'm guessing Edo Tensei ninja should be pretty strong at the start of the battle.