Having used Yanma before, I agree it's a thoroughly miserable experience. You really don't get anything until Air Slash and Bug Buzz.I wrote this in the previous thread (too lazy to find and redirect), but why in the good name of Satoshi Tajiri you people insist on putting Yanma on anything higher than E? I legit question if you have ever used it. Saying from experience (and openning to the possibility that I used it wrongly), the incredibly pathetic dragonfly should not be anywhere above E (hell, even F if people really think Swinub is bad). I'll use the criteria established by the OP to argue my point below:
1) Availability: Yanma is a Great Marsh mon, and that itself is bad news. Worse, it's a conditional Great Marsh mon with a flee rate of 47.1% according to Bulbapedia. While Great Marsh is somewhat mid-game (I tried to get it before Maylene), the safari-esque nature of it is extremely unappealing.
2) Typing: Bug/Flying is bad defensively. Very bad. The tons of Zubat line used by Team Galactic and weird abundance of Steel and Flying types accross the region is a chore to deal with. Offensively-wise, the STABs are not that bad, but you won't have it until VEEEEERY late unless you undergo various tedious and/or unorthodox steps that I'll explain below.
3) Stats: Trash dragonfly base form is a glass cannon that shoots a tiny amount of water. 65/45/45 at the time you get Yanma is not that good, and 65 Atk is not really enough. 75 SpA is bad, for reasons I'll go over below. What could be the saving grace of the bigger trash dragonfly, that sweet sweet 116 SpA with a not-shabby 95 Spe (which can be boosted if you opt/find one with Speed Boost), not all muscle can make a hit with a cotton ball hurt. If you want the full experience of using Yanmega, you'll have to trust that average 76 Atk, which is surprisingly enough lower than anything in its rank and above, and the tier below! 86 Def with 86 HP is nice though, I give you that. You may think yourself: "Why, I will only use Special moves, you idiot!" Well...
4) Movepool: When taking consideration how Platinum works in terms of level curve and the finishing points of the game, Yamna has to have one of the worst level up movepool and curve in the game. I will just post the screenshot of what and when it learns by level (again, thanks to Bulbapedia)
The major difference between Yamna and Yanmega is when the latter learns Feint and Slash, the former gets Hypnosis and Wing Attack (arguably better moves).
Now, I'll be a reasonable person and expect that, by the time you reach Volkner (whose team ranges from 46-50), you'll be at least at level 45, as it was my case. In that scenario, I beg my reader to please explain, by using only level-up moves, how the hell you managed to level up that much with that atrocity without switch-training of infinite rare candies? Seriously, you get it (after the hassle at Great Marsh) at level 27-30, so Yamna by start will have Detect, Supersonic, Uproar and either Sonic Boom or Pursuit. And spamming Uproar in midgame Platinum is not the best nor brightest idea. As you reach level 33, you ditch Detect for Ancient Power and evolve your trash dragonfly. You then rush to test it out your new 60 BP, 5 PP unstabbed move, you realize how 116 SpA means squat if you have no way of using it. And then cry realizing you'll only have an usable special move at level 54 (thanks FEINT!)... unless you use that moderately adequate 76 Atk and your heart scales for Bug Bite and Night Slash. OR, if you decide to evolve it at level 43, it can have Wing Attack instead!
Now, of course it's highly unlikely that you're not gonna waste at least one TM in Yanmega, which already reminds you with the "Dumping non-renewable resources on one Pokémon is considered highly inefficient for the purposes of this list". So, what our garbage bug can learn? Long story short, the useful special moves are Hidden Power, Giga Drain, Hyper Beam, Psychic, Shadow Ball, Silver Wind and Dream Eater. Hidden Power is a gamble and relying on it says a lot about the Pokémon. Having to resort to Hyper Beam really makes me question why are you using it other than anything else. Shadow Ball is one-time only before Frontier, but if you have nothing else to use on the way to Celestic, Yanmega can use it (I saved it for my Glaceon so I have no experience with). Psychic is either too late or requires too much time/money in the Game Corner, and Dream Eater is unusable unless you evolve at level 38, in which case good luck with that consistent 60% move. Giga Drain is usefull, I guess, but I didn't use it on Yanmega (saved for other) and I suspect it has the same problems as Ancient Power. The only option left is Silver Wind, which you get relatively at the same time that you catch a Yamna at Route 212, and the route I went with. You NEED that move to even scratch enemies, and although the boost is nice (when it happens), Silver Wind + Ancient Power (if you don't use any other move) is only 10 PP, so you are good to go for 10 battles on the best case scenario. You cannot compare Yanmega with the 30 PP and 80 BP Bronzor/zong, which albeit slower will probably win on tankiness, and even a lot of D such as Marill and Tangrowth (one that should be at C but I'll go over in another time). You can go physical with Aerial Ace and lol Steel Wing, however.
So that leaves us with Move Tutors, right? Again, courtesy of Bulbapedia:
The tutors that I cut in the image are the postgame ones, so no Signal Beam for you. If you can afford Shadow Ball, you are not using Ominous Wind. Even if you're using Shadow Ball on something else, you're not using Ominous Wind for the sheer fact that not only is another weak move with almost no PP, but the cost is too much. Unfortunately, that cost is the same reason why Air Cutter is a questionable option. Not relying on chance, you'll not have without backtracking A LOT in the game all shards required for the 55 BP move. You could soft-reset and clock manipulate at Pastoria to get all shards every day, or be lucky at Underground, but by that point you realize that raising a Yamna is quite a lot of, paraphrasing the OP, "[...] a hassle".
5) Major battles: You'll probably beat Maylene's Meditite by spamming Uproar. I did... If you go outside your way to teach Air Cutter, you might even beat Machoke! If you teach it Giga Drain then Wake's Quagsire can be manageable. Other than that, Aaron and Lucian can be a cakewalk... if you reach level 57! Don't bother with anything else unless you picked Empoleon, then Torterra is manageable with Silver Wind.
Concluding, I am yet to see anyone who used Yanmega and had a different experience from my miserable one. Trash dragonfly may be BL in the generation it was introduced, but in-game it deserves all the stinkiness that its pre-evo got since GSC. Yanma and Yanmega are horrible Pokémon and keeping them anywhere above E or even F are an insult to people that experiment with Pokémon.
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I had to make it level 57 because I was really annoyed at the lack of Bug Buzz. It was a prideful thing to do. Also I named it Episode I because "Star Wars - The Phantom Menace is the most disappointing thing since my son" (PLINKETT, Harry S.), the exact reaction I had using Yanmega. Everything else on the team except Empoleon (A), should range between B and C. And I agree with everyone that posted here that Glaceon is good, way better than where it's shoved at, and certainly MUCH, MUCH better than Yanmega.
Matter of fact, Air Cutter is almost mandatory for any kind of route clearing. And as we know, Shards aren't quite quick to come by. The payoff is not exactly remarkable, though Lucian doesn't want any of that smoke.
E sounds like a good place for it, F if it's hard to catch, been a while.
