[+2]: Chandra, Pyrogenius deals 2 damage to each opponent.
[−3]: Chandra, Pyrogenius deals 4 damage to target creature.
[−10]: Chandra, Pyrogenius deals 6 damage to target player or planeswalker and each creature that player or that planeswalker's controller controls.
In a Two-Headed Giant game, Chandra's first ability causes 4 damage total to be dealt to the opposing team.
The last ability of Chandra, Pyrogenius doesn't target the creatures. A creature with hexproof the target player (or controller of the target planeswalker) controls will be dealt damage this way.