The castform is just...ugh. Needs work. Work on the outlining, tail, and head.
From left to right: Hoppiler, Rollip, Suckeeto, Tuttby, and Coyoco.
One thing I notice instantly is that the outlining in general is dark. And I mean really dark. While I understand the newer style of sprites does generally have dark(er) outlines too, yours are a bit too excessive. I mean, Coyoco for instance is a great example. The wings still use a dark grey outline and a black/darker grey outline. Here's Yanmega from B/W
Even Yanmega's wings are lighter. If you want to emulate Game Freak's style, Yanma and Yanmega are great examples for fly-like Pokemon.
The shading ranges from being used quite effectively (e.g.: Sucketto- the head has been done pretty well imo) to a bit excessive which kinda ruins it. Again, looking at you Coyoco. The head and back with the light, medium and dark shades are just unnecessary imo, and I think removing the lightest shade would help make it a little more natural. I even thought it was reminiscent of pillow-shading (I know it's not, don't worry ;)) at a first glance.
One last thing I'd like to mention is that really the Pokemon shouldn't be directly facing the player- rather they should be alligned to the left. Goppiler for instance is obviously facing the completely wrong direction, and Rollip and Suckeeto succumb to this problem a little bit. Suckeeto probably
could get away from it but it's probably best if you move the eyes a few pixels to the left and maybe align the ears a little to the left too. Rollip seems to be completely gacing the player however.
The only Pokemon I can reaaaaally think of that is strictly facing the player is Clefairy:
However, this was just for one pair of games and in the subsequent generation it was again completely facing the left so... :\
It's an iffy one but I would advise that all Pokemon should be faced to the left in the future.
Anyways, I do really like the designs! :D They're very unique (a grasshopper Pokemon? Yes, just yes :D) and I do like your style apart from the issues I mentioned. Tuttby, for instance, really emulates the newer Pokemon's styles well and I really like it. :D Keep up the spriting! ^^
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Anyway, I revamped one of my earlier Pokemon. While I do not have an image of it on its own, it is part of this FakeDex:
http://superjub.deviantart.com/art/New-FakeDex-WILL-BE-REGULARLY-UPDATED-301887976 It's the turtle with the blue shell. :) Anyway, I decided it was a bit bland, boring etc. so I tried to spruce it up a bit with BRIGHTER COLOURS (!!! :DDD) and a different shell. It also has an official name now (Tortosus) so yeah. :)
Tortosus (tortoise & colossus)
The Tortoise Pokemon
Water/Rock
"The huge shell on Tortosus' back is used for surprise attacks and camouflage from predators."
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C&C is appreciated! :D