In another attempt to make the game more "fun", Zynga added extremely unbalanced bosses in Las Vegas and the new Beat the Feds challenge.
Beat the Feds
On gold, these are brutal and DEA Iverson and DA Embry are the worst. The trick is to stack stamina and use consumables.
Since Feds don't regenerate stamina, the only useful consumable is the shiv. Grenades do too little damage while the shivs were doing more damage than my regular attacks.
Have friends send you a lot of shivs. Accept 10 and keep the rest in reserve. Accept another 10 after you use the ones you have, etc.
For stamina, make sure you start your fight within 4 hours of leveling and your next energy pack and make sure you level before using the energy pack. Have 5 crime spree requests primed as each will give you 40 stamina.
Install the toolbar. Hopefully, you'll get the 200 stamina refill or the 25% energy recharge. At worst you'll get 200 energy.
Here, the 2 nasty bosses are Juliana "Black Widow" Trieste and 'Red' Jackson.
In this case, it's the stun guns which are crucial. Shivs and grenades are great for getting rid of henchmen but will do little damage to the boss. Stack a lot of stun guns, again accepting them 10 at a time.
Don't bother wasting time on health refills as the help they provide is too insignificant when compared to the stun guns.
While in Beat the Feds, you'll need very powerful allies to help you do any kind of damage, Las Vegas bosses' attack and defense seem to depend on the attacker so any one of your allies will prove useful.