Source: Races of the Dragon
You can use your breath weapon to create an entangling mesh of energy.
Prerequisite: Dragonblood subtype, breath weapon.
Benefit: When you use your breath weapon, you can choose to enmesh all creatures in its area instead of producing its normal effect. Your breath weapon deals only half its normal damage; however, any creature that takes damage from your breath weapon becomes entangled and takes an extra 1d6 points of damage, of the same energy type as normally dealt by your breath weapon, each round at the start of your turn. This effect lasts for 1d4 rounds.
If your breath weapon doesn't deal energy damage, creatures damaged by the initial breath are still entangled but don't take additional damage on later rounds.