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.