My proposed solution is to give the Natural Explorer options each a defensive or utility (mostly movement) buff that is useful more often, and to give Favored Enemy a generally useful offensive buff.
So, lets throw out some specific ideas. First, just for fun, you are acclimated to the environments represented by your favored terrain.
Arctic - Cold Resistance
Coastal - Swim Speed and ability to hold your breath, maybe an extra bennie since this is still pretty situation? Ignore difficult terrain from loose earth?
Desert - Resist poison, ignore difficult terrain from loose earth
Forest -
Grassland - speed buff, buff to stealth while prone (ie crouched in the tall grass)?
Mountain - climb speed?
Swamp - resist poison or acid or necrotic?
Underdark - darkvision or increased darkvision?
Favored Enemy
Expert Hunter. You know how to bypass the defenses and special abilities of a group of potential enemies. You gain proficiency with Poisoner's Kit, or Herbalism Kit if you already have it. When you make a poison, your favored enemy has no true defense against it. If your favored enemy has immunity to poison damage, it instead has resistence against damage dealt by your poisons, and if it has resistence normally, it loses that resistence. Likewise, if it has immunity against being poisoned, it instead has advantage on saving throws against the condition, and if it has advantage, it loses that benefit against your poisons.
Additionally, you can make a number of specialized poisons equal to your proficiency bonus as part of a long rest. You can make more as part of a short rest, if you spend a spell slot to do so.
Aberration
Beasts
Celestials
Constructs
Elementals
Fey
Fiends
Giants
Monstrosities
Oozes
Plants
Undead
Humanoids
Dragon - slow target, impede fly speed especially, possibly cause target to take poison damage when it uses a breath weapon
Gotta go to work, more ideas later!
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