Angelo's third special bow attack tops my list of "most useless attack in DQ8". Supposedly, Needle Shot is a 1 MP attack capable of killing an enemy in a single shot. However, I have never once actually seen this happen. On top of that, Needle Shot only does 1 point of damage if it fails to kill its target, which is pretty useless. In comparison, Yangus has a scythe attack called Grim Reaper that not only launches an instant death attack against an entire group of foes, it actually works and does full regular damage if it fails to kill instantly. Needle Shot is made even more useless by the fact that Angelo himself can cast a fairly reliable group instant death spell naturally. With clearly superior alternatives abound, Needle Shot is simply a poorly thought out ability.
On paper, Yangus's first Hammer move, Heart Breaker, seems good. It is a 2 MP attack that does full attack damage to an enemy with a chance of "shocking" the enemy, causing them to lose one turn. However, like Needle Shot, Heart Breaker has been useless to me simply because it almost never does what it is supposed to do. Despite using it against every boss and strong enemy I have ever come across, Heart Breaker has only worked once or twice. Furthermore, the 2 MP cost make the move too expensive to use on a regular basis, since Yangus has very limited MP. In contrast, Jessica has a very similar move called Blow Kiss that not only can be used with any weapon, it is both free and much more reliable than Heart Breaker.
One of the hero's sword moves, Metal Slash is on this list because I haven't found a real point for it yet. Supposedly, it is effective against Metal enemies, but it doesn't do any extra damage against most enemies with Metal in their names. It seems designed to help kill Metal Slimes (rare enemies with incredibly high defenses, but only 5 HP), but the one time I cornered Metal Slimes, Metal Slash did only 1 point of damage, the same amount of damage my other characters were capable of doing. While it apparently lets the hero hit the highly evasive Metal Slimes easier, it is way too limited in scope to be useful.
Fire Slash and Dragon Slash:
Along with Metal Slash, these two moves were among the hero's first three sword abilities. These have actually been useful. While I rarely used Dragon slash due to the lack of dragon-type enemies in the early game, I found that plenty of enemies were weak to Fire Slash. Both moves could even be used for free. Unfortunately, both of these moves are on the list thanks to the existence of Falcon Slash. Falcon Slash lets the hero attack twice in one turn with slightly reduced attack power. On average though, Falcon Slash will do more damage to an enemy weak against fire than Fire Slash, and Falcon Slash is still free. If Falcon Slash actually cost MP, Fire Slash and Dragon Slash would not be on this list.
This 2 MP Whip attack lets Jessica heal herself slightly by doing damage to a group of enemies. Unfortunately, it only heals Jessica by 13% of the damage done to the first enemy she hits. Since Jessica can only do 30-40 or so points of damage, she can only normally heal herself for 3-4 HP with this move. In comparison, Angelo can use his Cherub's Arrow attack (a 0 MP Bow move) to heal 3-4 MP with each shot, which he can then use to cast Mid-Heal or Full-Heal. Jessica is better off saving the MP for attack or status spells.
Yangus's second hammer move, this one costs 2 MP to steal 10% of the money the enemy normally drops in addition to a regular attack. Since most enemies only drop chump change, this attack will only give the part 2 or three gold coins per hit. Once again, Yangus's MP is too low to be squandered recklessly on normal enemies. In comparison, I use Yangus's Steal Sickle a lot, despite its horribly low success rate, because it is free.
A common problem among many of these moves and other is too low of a chance of success, or too little effect. In addition, other characters often have clearly superior alternatives. So while the characters have plenty of special moves, I find myself relying on only a few (Falcon Slash, Wind Sickle, Cherub's Arrow, and Twin Dragon Lash) most of the time. I might talk about these abilities some more after I have seen the rest.