Raghu,
If you talk about adharma being adopted by Arjuna doing the war,, the list is endless :
1. Bhishma .... was defeated ( but not killed ) through the shield of Shikandi...
( I had written a posting on the background of Shikandi )
2. Drona... Was about to use Bramastra and destroy the entire pandava army when ... under Krisha's advise.... Bhima will kill an elephant by name Aswathaama and shamelessly tell Drona that he had killed Aswathama... Drona .... for him ... Aswathama was life and he will reconfirm with Yudhistira who will also shamelessly say that yes... Aswathama is killed... but in a mild tone.... an elephant... Drona will not hear the second sentence of Yudhistra and will give up arms and will lay in yoganishta when Drishtadyuma will cut his head..
3. Karna..... You know the whole story...
Karna's curse was momentary as he will forget all the skills what he had learnt from Parasurama... but Arjuna could never have killed Karna as he is equally matched in skills...
Arjuna had to kill him while Karna was trying to lift his chariot wheels.
4. Duryodhana...... The whole world knew that he cannot be beaten in mace fight..... and as per the war rules.... one should not hit before hip.....
Beema ... under the advise of Krishna will hit his thigh and he will also collapse.
5. I have mentioned already about ... Poorisiravas.
6. Bagadhathan was an old brave warrior... and known for elephant fighting and is a specialist.... Due to his ageing... he will wear a cloth to hold the extra flesh which was coming before his eyes....
At one stage. Bagadhatha will use the Ankush and chant Narayan astra... and will throw at Arjuna... but krishna will appear before him and will absorb that astra... .WHICH OTHERWISE WOULD HAVE KILLED ARJUNA INSTANTLY.
As this was Narayana Astra... Sri VIshnu's astra.... Krishna happily will absorb it and will protect Arjuna.
Arjuna will cut the cloth which was protecting the eyes of Bagadhatha...
This will make Bagadhathan virtually blind as he will not be able to see anyting.
At this time... Arjuna will send an arrow which will kill Bagadhathan....
The above are all what pandavas did....
The one adharma what Gauravas did was.... killing abimanyu as a group .... when he was without arms.....
But for this episode... the war was won by pandavas purely but wicked and adharma methods...