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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.)
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.
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.
