Wolf in the Woods
Green dragons always nest in deep forests making them favor attacking on land jsut as likely as from the skies. This is actually a blessing and a curse for would be heroes as a dragon on the ground is always safer than one strafing attacks from the sky, but this isn't simply any land this land will bend to the dragon's wishes. Masters of plants a green dragon fills its forests with dangerous thorn covered plants to direct its prey where it wishes while allowing such plants to clean themselves for its own path only be be replaced when the dragon has moved on. This combined with the green dragon's massive intellect creates an enemy that wants to play a game of chess with a worth hero, but will frequently and openly change the rules in its favor because well this is its game and you are jsut something to play against.
As I've said before a dragon's breath weapon says a lot about how that dragon operates and this is just as true with the green dragon. The funny thing is though a green dragon's breath actually tells more about what they aren't much more than what they are. Their breath is a poisonous cloud that billows out in a cone. At first glance this would look like a beast that makes sweeping attacks trying to engulf as many opponents as possible, but with ti being poison this actually tells us that a green dragon has to know its enemy very well before using such an attack. Poison damage (at least in D&D) is one of the easiest damages to over come with many characters being able to take only half damage and some (looking at you monks) can ignore it completely. This means that a cocky green dragon might find themselves in a tight spot coming full force at a hero that can just shrug it off as if it were nothing.
Green dragons always and I want to repeat ALWAYS play the long game. They lurk in hiding assessing their threats before striking. If they are ambushed they will face defeat if it means they will survive even to the point of accepting servitude to foes that best them. To a green dragon this is a calculated loss, only to them it isn't even a loss. A green dragon will "accept" servitude as a way to get closer to a worthy enemy taking that time t gain as much insight in their foe as possible. They will take their time to find our greatest weaknesses to exploit and if you think that simply means waiting for a moment to kill them when they are sleeping or otherwise unaware you are forgetting that cruelty that makes a dragon a true threat. If a green dragon has taken the time and energy to pretend to be a servant then simply killing you would be a kindness.
A green dragon only kills its food and creatures it sees as no more than a pest. Anyone else that a dragon deems "worthy" enough instead suffers a much worse fate. A green dragon is almost like a cat with a mouse, if that cat was pure evil and possessing tremendous power. Green dragons often leave survivors from even the weakest of groups looking to challenge it just to put fear in its heart. They push the limits of fear and pain simply to see when a creature breaks. Those driven to near madness will be pulled of any information the dragon might find useful about where they came from to see if they would also make good "play things". Finally once a toy is broken to the point of lacking any more forms of amusement to the dragon will it finally kill and consume the emotional husk that remains.
Green Dragons are almost the serial killers of the fantasy world with a cold calculating mind. They play slow and careful and only if they are dead do they consider themselves defeated. Throwing one of these at your party so involve the planning and foresight that that dragons themselves posses and in capable hands can stretch out into a long horrifying adventure.