Toxic Iguanar has deathtouch as long as you control a green permanent. (Any amount of damage a creature with deathtouch deals to a creature is enough to destroy it.)
2/1/2009 As long as at least one permanent you control is the specified color, the ability will “work” and grant this creature the bonus. Otherwise, it won’t have the bonus.
2/1/2009 Whether Toxic Iguanar has deathtouch matters only when it deals damage (that is, at the point when its combat damage resolves, or at the point when a spell or ability that causes it to deal damage resolves). For example, if your only green permanent is a creature that receives lethal damage at the same time Toxic Iguanar deals damage to a creature, the deathtouch ability will still apply and the creature Toxic Iguanar dealt damage to will be destroyed.