Well, Skeelz and Freaks are both somewhat good against Piranhas because they have weak bonuses and so losing them doesn't matter. I don't have any decks on hand that are specifically anti piranhas but in the past I found a freaks half worked well when they had Smokey and were more popular.
Also, you could try just adding a protection: bonus card to what ever you are using if there is a good one.
GHEIST is a difficult matchup for Piranas because they have high damage and easily do 2 hit KO. I play Piranas a lot and GHEIST is the clan that consistantly gives me trouble.
The best advice against Piranas is to play with any SOA you can- it's crucial to be able to stop their pill manipulation. If you choose a clan that has a good SOA, so much the better. DR is also good- the key to beating Piranas is high natural damage and minimizing their damage, and trying to win at least 2 rounds. Then avoid:
6 power characters, especially 4-5*- these get wrecked by Tula.
Avoid clans that are over-reliant on their bonus- Rescue, Montana, Junta, Fang Pi, Bangers, All- Stars, Vortex.
Avoid Nightmare because Piranas dominate that matchup.
I suppose some other fair choices are Uppers, Junkz and Sentinels. Uppers have amazing damage and Rubie is a wrecking house against Piranas. Junkz have good abilities and fairly high power- same with Sentinels, plus Lehane dominates both Tula and Hawkins. The 3 top Freaks (Grudj, Bogdan and Olga) are all good against Piranas but without poison their combined damage is weak for 11*.
Cards with high power and/or SoB as an ability dominate piranas - for instance lehane and Gibson. Piranas as a whole in general lack in power, so clans that have high power (7- and bonus independent will do ok - examples of such clans are Freaks (Bogdan Grudj Olga, as Kitsune mentioned), and Jungo (They're staples all have 7 power or better - Askai Mindy Scopica Nyema Radek Pegh, Buba etc.) . Skeelz is also a good choice - they have many cards at 7-8 power. (Sasha, Tomas, Manfred, Chiara, Corvus, Danae, and Cley can reach 8 power too)
Piranas lack a good SoA (Spycee is usable but not optimal), so you want to use cards with beastly abilities - again Freaks, Skeelz and Jungo come to mind, along with maybe La Junta (their support: abilities and power manip is pretty decent). Nightmare have a couple of good abilities, but they have mediocre power, so they lose to Piranas' pill manip since Piranas can afford to overpill.
The thing about Piranas is that unless you draw their high gap 5 stars (Selma/Bloodh), you usually have to win 3 rounds to win the match. If you can get some damage in while defeating a big card (such as Scrubb), they can't catch up if you have a DR - Pill manip becomes almost useless when you have no pills anyway.
Piranas generally have only average power and damage, and prey on overly bonus-reliant clans like All stars and Rescue. That means clans with good base power/abilities and lousy bonus fare well against Piranas. So Skeelz, FPC, La Junta, Freaks, and Jungo all have an advantage, and clans like Sakrohm, Junkz and Sentinel can fight on an equal footing.
Its really hard opposing SoB clan, Piranas and Nightmare... So how about use one of those clan?? At least you can also use the clan in countering other clans..
Or use clan with characters that's not reliant to there bonuses.. Those with good base power/abilities, like what the above said..