When your character is low on health, they start glowing (or in Bee’s case, exploding) and gain additional abilities. Here’s a list of desperation effects:
ANBU Kakashi: <X modechange special can be performed at 0% chakra, although it consumes all your chakra
Ino: Gain <X special. Fires a projectile that confuses opponents, costs 25% chakra.
Choji: Take half damage during vA. Gain power armour during vA.
Shikamaru: Gain ludicrous amounts of guard. It’s essentially unbreakable in normal play.
Asuma: Charged kunai become unblockable
Sakura: vA modechange no longer drains chakra, although you still can’t gain chakra while it’s going
Naruto: <X modechange becomes free
Sai: ^A birds return from behind opponents a little while after leaving the map.
Yamato: Can use <A counter as a regular move for 25% chakra.
Kiba: Akamaru becomes ready after attacking much faster
Shino: Bug attacks drain chakra on block
Hinata: <X modechange special becomes free.
Kurenai: vA gains larger radius of effect. >A becomes free. She’s still bad.
Kabuto: Regenerate half the damage taken from any attack. As a side-effect, Kabuto becomes immune to chip damage.
Anko: <X modechange special becomes free.
Orochimaru: <X counter special becomes free.
Tsunade: vX healing special can be activated without connecting with an opponent.
Jiraya: vA attack becomes the size of Africa.
Sasuke: <X special changes from fast, unblockable, short-range burst to a blockable special that hits opponents anywhere if they’re doing something after you use it. Basically it makes him worse. Also his sword attacks do more damage.
Itachi: <A teleport becomes free.
Kakazu: X special trigger attack changed from a kick to a very fast, medium-range lightning bolt. Can also hit more than one character in some situations.
Hidan: Gain power armour performing vA. Half the damage you take is reflected to opponents while standing in vA circle.
Deidara: Clay attacks no longer drain chakra, but they still require chakra to perform. >A bug continues crawling along the ground instead of just exploding.
Sasori: All attacks poison opponents.
Hiruko: All attacks poison opponents.
Yugao: Sword attacks do more damage.
Tenten: No longer drops weapons when taking damage.
Neji: >A pokes drain chakra on block. <A counter drains chakra at half the rate when held. X special gains 360 degree tracking.
Lee: <X modechange becomes free.
Gai: Gain <X stomp attack.
Kakashi: <X modechange becomes free. No longer lose health when Sharingan open.
Killer Bee: Gain <X burst that puts you in the invulnerable state while it occurs, for 25% chakra. Upon entering desperation, Bee immediately uses the attack for free.
Kisame: vX special does much more damage. vX special can be used at 50% chakra, but drains up to 75%.
Gaara: Can block unblockable attacks. Gain retroactive counterspecial for 50% chakra – just press X in blockstun. A sand projectiles are always thrown fully charged.
Temari: <A summon no longer drains chakra while it’s out.
Chiyo: <X chakra shield drains at half the rate. vY puppet-summon makes puppets teleport to her location
Baki: >A wind blades become much larger
Minato: Gain vX and <X specials. vX places a marked kunai, <X teleports to the kunai for 25% chakra, even out of movelag. <X with no kunai goes straight to idle animation for free. Yes that gives Minato an infinite.
Sage Naruto: Rasengan attacks no longer drain chakra, though they still require chakra to perform.
Raikage: Negates ranged attacks while charging attacks. This includes some specials. Also reflects kunai and needles.