Conclave of the Marshwarden.

Marshwardens take their cues from natures most challenging terrains and capable amphibious explorers. In doing so, these rangers become world-treading athletes with powerful magic toxins at their disposal. Marshwardens often seek to protect the worlds most endangered subjects and dive headfirst into new challenges, knowing full well that no matter what obstacle stands in their way, they almost certainly have the means to overcome it.

Level 3 Feature:

Marshwarden Magic.

Starting at 3rd level, you learn an additional spell when you reach certain levels in this class, as shown in the Marshwarden Spells table. The spell counts as a ranger spell for you, but it does not count against the number of ranger spells you know.

Amphibious Alacrity.

When you choose this archetype at 3rd level, you gain a climbing speed and swimming speed equal to your walking speed, and you can hold your breath for a number of minutes equal to five times your ranger level.
Starting at 7th level, you can jump your full long jump and high jump distance, with or without a running start. When you reach 11th level, you gain the ability to move across liquids on your turn without falling during the move.
When you reach 11th level, you gain the ability to move across liquids on your turn without falling during the move.

Toxic Strikes.

Beginning at 3rd level, you ignore the loading property of blowguns, and attacking with a blowgun at long range does not impose disadvantage on your ranged weapon attack rolls with it. Further, when you are hidden from a creature and miss it with a ranged attack using a blowgun, making the attack does not reveal your position.
In addition, your strikes are magically toxic. Once per turn when you hit a creature with an attack, you can deal an extra 1d6 acid or poison damage to the target (your choice). This extra damage increases to 1d8 when you reach 11th level in this class. When you deal this extra damage with a blowgun or dart, you can treat the dice for this acid or poison damage as having rolled their maximum value.

Level 7 Feature:

Poisonous Defence.

Starting at 7th level, when a creature successfully physically grapples or restrains you, it takes acid or poison damage as if it was hit by your Toxic Strike. The creature takes this damage again at the end of each of its following turns that it continues to grapple or restrain you.
In addition, when an attacker that you can see hits you with a melee weapon attack, you can use your reaction to cause it to take your Toxic Strike damage, plus bonus acid or poison damage equal to half your ranger level (rounded up). You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses of it when you finish a long rest.

Level 11 Feature:

Crippling Toxins.

At 11th level, whenever you deal damage from your Toxic Strike or Poisonous Defence feature, the targets speed is reduced by 10 feet until the start of your next turn.

Level 15 Feature:

Unstoppable Marshal.

By 15th level, you have immunity to poison damage, and you are immune to the poisoned condition.
Additionally, you are always under the effects of the Freedom of Movement spell.