Decided to give it another go at the Sacred Stones banner in Fire Emblem Heroes. I was hoping to get Amelia because I keep hearing how great she is in this game, but on my very first pull, I got this instead:
Yep, a 5-star Tana! Her stats are 25 Atk, 10 Spd, 6 Def, and 6 Res. On the one hand, I do need more blue units on my team, so she is a welcome addition in that regard. On the other hand, Tana also has Moonbow, so she makes great inheritance fodder. Decisions decisions...
You got her as +Atk -HP; if you sacrifice her for
Moonbow of all things, you're insane.
Seriously though, she is one of the best lance units in the entire game, flier team or no (and you have a really good boon and bane on her), and even if you did want to use her for skill inheritance, Guidance is infinitely more valuable than Moonbow which is on like a dozen other units, and is honestly vastly overrated in my opinion anyway (its only appeal to me is its low cooldown, or if you find yourself facing a lot of bulky units like Lukas or armoured units).
Ribbon Girl's jumps are pointless because there's no benefit on staying up in the air for so long, Ninjara's is flashy but whether or not it's there won't change if you get hit or not, I didn't understand or was able to use Minmin's, Helix's stupid jump just makes him easier to get hit and Twintelle's is "what if we put Peach's Float in a ground based fighting game?". Didn't play the others.
The arms never did anything different, they all just punched with different speeds, the electric and ice ones never did what they're supposed to, shield never blocked anything, slap-whatever is just a faster punch and the others just do an arc before hitting. The only one I felt did something different was the Dragon Arm tbh.
Min Min's special technique is, if you dash and hold the button down, her left arm changes into a dragon, which gives her the largest arm girth in the game (arm girth affects the size of your ARM's hitboxes; the larger it is, the better), and her left ARM will be permanently charged (until she gets knocked down, that is). It's really powerful once you figure it out. Her other technique is, if she dodges backwards on the ground, or in any direction in the air, she will perform a kick which can block incoming attacks. Pretty useful once you get the timing down.
As for Helix, he is really not beginner-friendly at all. Probably takes the most amount of practice to get the hang of when to make him grow taller, or shorter, or whatever. I doubt very many people will figure him out in the few days the Testpunch is up for, but once you do, he can be pretty strong. Apart from the Ice Dragon, though, his default ARMS are pretty lame, and he needs custom ARMS to be most effective.
Twintelle's effect is actually a kind of bullet time that slows down incoming punches; you can use this to dodge out of the way, and then attack when the opponent is left open. It's pretty annoying when used effectively, since it basically lets you control the pace of the match, and forces the opponent to slow down so they can try and punish your landing.
I'm not as familiar with the other two you mentioned, so I can't comment on them, though Ribbon Girl's jumping ability is why she's considered one of the strongest characters in the game, and generally you actually do want to stay in the air with her.
As for the electric/ice ARMS "not doing what they're supposed to", you need to charge them first before they have the electric/ice effect. Charging ARMS is key, and the tutorial really doesn't explain this well, so I can understand why you would have missed that. To charge your ARMS, you can either dash, block, or jump (blocking or jumping is quicker, but the charge wears off more quickly). Charging ARMS is especially important for Min Min, like I mentioned before, since otherwise she will have difficulty landing hits at all.