I've beaten the game a few times on Classic, and it's easy to see how they could make it harder without having to something something Baldur's Gate casuals per-rest Van Buren Gamebryo health sponges Chris Avellone console commands Planescape Torment Obama hasn't even leveled a Tauren
Fixing resting: No resting in dungeons. Or limited resting in dungeons. Boom. Bill is in the mail.
Fixing dungeons: Every level in a dungeon (or just every dungeon) is one encounter. So, no end-of-battle-health-regen/spell refresh/resurrection til you clear it.
Fixing enemies: Fampyrs are easily the hardest enemy in the game. Why? They dominate you (Intellect Affliction.) So, more enemies that use high tier afflictions in extreme ways. Leeches that tank your Might and force you to win quickly or find an alternative to beating them with damage. Timelords that steal your Dexterity to run circles around your goofy ass. Mindcrushers that eat your Resolve and then start gangbanging you with spells. Ex girlfriends that drain your will to live.
More enemies that exploit your strengths or game mechanics in general:
Ethereals that you can't damage with high PEN.
Spell-immune enemies that redirect your magic away from their friends and on to them.
Enemies that can transform into other types of annoying enemies.
Enemies that penalize you for killing them in the wrong order by exploding.
Enemies that enclose your buddies in temporarily impenetrable cages to prevent them from helping you
Enemies that teleport your guys with the best buffs out of position.
Enemies that eat their dying allies for a nasty buff before you can finish them off.
Spell junkies that can fire off casts at an insane rate who will eventually erupt for a huge AoE if you don't kill them fast enough
Liches that grow more sexy with every one of their underlings you kill
Gunslingers that drill you with lightning quick trigger pulls as long as you can't reach them in melee
Sorcerers who destroy spells in their grimoires to fully heal themselves
Soul Savagers who self-inflict damage in order to deny you an ability or spell for the rest of the encounter
Savvy swordfighters that easily knock down characters using non-proficient weapons.
Shockwave specialists who prone tanks with ease
Mirror Ghouls who take the form of one of your party members
Whispers of the Past that attack you as 3 clones of you from before you leveled up
Parry Bois who have a high chance to block and counter auto-attacks
Medal Considerants who are at their best when fighting your highest-performing party member
Drunked Blade Thwackers that sloppily lunge at you with no accuracy but devastating damage
Wizened Scribes who cannot be hurt or affected by the same attack or ability more than once
Dragon Haberdashers who randomly summon a legendary weapon at the beginning of combat
Melancholy Flautists that are healed or gain Might any time any character is healed
Locomotives that can only move and attack in high speed straight lines
Low accuracy high damage high speed enemies that die if they miss. Also, they're racist.
Enemies that teleport their allies to another dimension to heal
Conservationists that temporarily make your ranged units have limited ammo
Ooze Accountants whomst've take continuous damage in order to paralyze one of your manz
Isolators who teleport flimsy characters into closed one-on-one deathmatches
Edgy Hypocrites that are very effective against a defense that they have a very low score in
Shame Cyclers that do .2x damage normally but 7x when you're flanked
Michael Connors who steals your date to the dance AN HOUR BEFORE THE DANCE
Arcanists who can nerf schools of magic or types of weapons
Enemies that always doublecast/double attack but who also always get double attacked
Violent Idealists that hit hardest at characters that have dump stats
Opportunists that hit harder while you're in recovery
Marriage Marauders that make a member of your party impossible to buff
Misguided Advocates that replace your buffs with a different random buff
Shark Trackers that summon OP beasts that are also hostile to them
Vine Vagrants that respawn once with the weapon or ability that killed them
Overpowered enemies that buff you when you kill them
Enemies that do more damage if they've already knocked out one of you
MUSICAL GUEST: JUSTIN TIMBERLAKE
Pharmacy Reps that heal others when they die
Iron Spirits that copy the highest defense values from your party
Perennial Gentleman Callers that are unharmed by raw damage. Or hints.
Furnace Llamas that kill themselves to resurrect a friend
Enemies who take on the appearance of one enemy but the abilities of another
Spearflingers who do most of their damage at first contact with a singular highly accurate weapon toss
Smiling Insurance Salesmen who seduce your mom
Pork Porcupines Pork...pork... Perries that are much stronger when near allies
Nascent Spunk Demons who start dormant, harmless, and invulnerable but who eventually awaken as extremely powerful enemies if the battle goes on for too long
Hopeful Mormons that spawn if anyone in your party gets healed
Intervention Associates that negate your current attack but buff your next one
Enemies that spawn a random enemy when they die
Sloppy ****er Spaniels that negate the effects of a random piece of your armor
Gym Rats that debuff themselves to skip Recovery
Ego Lords that cannot be buffed or debuffed
Worthless Dance Attenders that ARE INVISIBLE UNTIL THEY ATTACK
Eye Communists that trade damage immunities with each other throughout the battle
My dad's expectations
Muscle Maggots who are faster and stronger if you've rested or waited recently
Inspired Thieves who copy one ability from each of your party members
Gonorrhea Goblins who heal your party members but sap their damage or penetration
Look at all this I'm basically already CEO of Obsidian.
Health potions, pet buffs, enchanting, and empower- gone. You gotta win with your weapons and skill and quicksaves alone.
Bonus mode with debuffs for classes and races:
Nature Godlikes take huge fire damage,
Fire Godlikes take more water crits and are far less effective at ship combat
Moon Godlikes are less accurate during the day
Death Godlikes be ugly af lol
Aumaua are inaccurate against small targets
Dwarves can't hit floating, flying, or hovering targets to save their lives
Priests can't do damage, (I see your angry comment fingers. These are just examples. chillllllllllllllll)
Paladins can't heal themselves and will be unable to attack enemies if there's a charmed ally nearby to gank instead
Each spell a Wizard casts in an encounter is progressively weaker
Rangers take huge penalties when enemies are in melee range,
Rogues have very low life and underperform when near allies,
Fighters have to take Constant Recovery as a subclass- no more pairing it with Devoted.
Non-Soul Blade Ciphers have abhorrently low body affliction defenses.
Soul Blade Ciphers are bad at spells? Idk these can't all be gems
Many enemy types can now silence a Chanter's phrases and invocations. "Hoarse" Chanters have to wait after casting Invocations.
Orlans are afraid of vacuums.
Druids cannot cast spells while shifted. Druids cannot use weapons. Druids are more easily Charmed by Wilder enemies
Rogues cannot wear heavy armor- are you writing this down?
Confused Monks begin to doubt their own existence and abandon the party to write F-Tier philosophy and bad fanfic (all fanfic is bad fanfc)
You should be able to be a tree