This one is easy. If it has less than 100 HP, you kill it.
This one is harder. One option is to have a list of effects (“Restore my allies” (instant long rest), “Grant me riches” (some large amount of gold appears, maybe with an enemy), “make me stronger” (character or ally gets a permenant buff). Another is to let it cast any 8th level or lower spell.
Are there no instakills in BG3?
In DDO I greatly enjoyed playing instakill builds as both a pale master wizard and a necro cleric. For a wizard focusing on necromancy (pale master) the main death spells were Finger of Death, Circle of Death and Wail of the Banshee, plus Power Word: Kill as a no-save enchantment spell with an incredibly long cool down. (210 seconds, compared to 8, 30 and 60 respectively for finger, circle and wail.)
For a necro cleric there was Slay Living, Destruction and Implosion with cooldowns of 8, 8 and 60. The issue for clerics was that Implosion is an evocation spell, so instead of just maxing necromancy and enchantment you also had to max evocation. But you really wanted evocation anyway for Blade Barrier.
All of the death spells could be nullified if the enemy had deathblock or death ward, including Power Word: Kill, so you might have to cast (Greater) Dispel Magic in order to land the instakill. And of course none of them worked on “named” enemies or bosses; only trash.
Are these spells not in Baldur’s Gate 3? If instakill builds aren’t really a thing in BG3, that bums me out a little. (Probably be 15+ months before it’s cheap enough for me to buy, but still.)
EDIT: Your point about wish is sound, though. DDO never implemented it.
Here’s the list of 9th level core spells, I think most of these are doable:
Aside from Power Word Kill, there are no instakills in 5e.
Aww, that makes me sad.
I agree that most high level spells could be somehow replicated in BG3 (though some are just super limited; BG3 Polymorph is super lame – where’s my Karlach T-Rex?) I think the issue is less “How to code it” and more the power ramp and what it means to the setting. Tier 4 play (levels 16-20) is supposed to be beyond “Save the city” or even “Save the world” and into existential threats to the cosmos/planes themselves and the power levels reflect that. It’s why you have characters like Elminster just float in and give some words of advice and handwave a reason why he’s not curbstomping the flight of dragons threatening Waterdeep. If you had realistic threats to a party of Tier 4 characters wandering their old home town, they wouldn’t have a home town any longer. BG3 makes some claims that the gods are worried or whatever but it’s ultimately a Tier 2 local-level adventure campaign.
Planning that stuff in a tabletop game is difficult when you have players who can trot around the Planes of Existence at will, for whom death is rarely more than a status condition and can reshape reality. In a video game context, trying to rein it in will feel very limiting. Or you cut out/neuter all the Wishes, Plane Shifts, Simulacrums, etc and just have the same stuff you were doing but with bigger fireballs. In which case, what’s the point instead of just making a new Tier 1-2 adventure?
There’s also the issue with casters rapidly outpacing melees by this point (You can teleport across worlds, I can swing my sword three times) though with all the equipment dripping with spell effects in BG3, that might be less of an issue.
I’m still in Act 1. An NPC gave me an item he called priceless, but then I go into his store and I see he will only give me 74gp for it. Maybe Laz’zel was right about him…
I’m not sure if this UI is obvious, but in the inventory screen there are 3 options for displaying your helmet or not.
Wish is a problem, unless you make it very very limited (like wishing for uber items only or something), but power word kill is just a high level save or suck spell, as long as your bad guys have decent enough saves it’s not game breaking. It’s definitely included in pathfinder: wrath of the righteous.
Traditionally, Power Word: Kill has no saving throw, but only works on creatures up to 100 hit points. Targets above 100 hit points are unaffected.
In 3.5 you also had to overcome spell resistance, which doesn’t appear to be a thing in 5e. This was meaningful in DDO because the first “epic” content (level 21+) began by fighting through drow in the Underdark to get from Stormreach in Eberron to Eveningstar in the Forgotten Realms. Drow spell resistance was no joke.
Wow, lots of good comments! Thanks!
I was going to say that Disintegrate could be an insta kill in 5E because it states that if the target is taken to 0 hit points, they are turned to dust. Sadly, the spell is all or nothing, which I think is terrible for a sixth level spell not to do some damage.
I can see them being done with BG3 and I always have it so that’s good. I was more thinking of high levels for high level spell slots and not the high level spells. Or more hit points. I never liked save or suck spells. I play my games to have fun and those aren’t fun for me and my groups.
I haven’t played DDO in a decade or more. What really did it for me was no ability to solo. I rarely find a group/guild that was on when I was, so if I couldn’t solo, I couldn’t really play. I don’t think I could finish any final boss monsters without a group. I also wasn’t excited about Eberron but that’s me.
I forgot that WotC’s research told them most games stop at twelve. That’s probably true for me. I want to go further (usually in PF1 but any DND like game) but when the story is done, I’m ready to tell the next story. Most DND/PF1 games do get ridiculous in the time it takes to do things at high levels, so I can understand groups wanting to experience it once, not like it, and avoid it later. Too many choices leads to analysis paralysis.
I admit that blowing up the smoke powder barrels to take out a Steel Guard is fun.
I loved DDO back in the day. Like you my main problem was being unable to solo or find a worthwhile group. I still have a soft spot in my heart for that game, though - my current tabletop campaign has the players working with the Sharn Syndicate to stop Daask agents from influencing an election, and one of their adventures was basically Waterworks (I stole the maps from DDO and all) with a Daask hideout at the end.
Some of you haven’t made it into Act III and it shows! 
There’s a part of the Temple of Bhaal where a cultist casts a Power Word: Kill on you with a five round cast time. He also has a shield that absorbs five hits before he can be damaged/affected. You’re supposed to make it through a gauntlet of assassins to reach him. I died once then just invis’d everyone to run to the base of his tower, snuck my See Invis rogue up top and waited for the cultist to fail his check and be visible, multi-attacked him enough to take out of of his shield charges, and he then teleported to the bottom of the tower where the Karlach, Gale and SH beat the shit out of him.
I got like 150 hours in this and the furthest I’ve gotten is the party after clearing the goblin camp.
I don’t even know this Orin you are spoiling us about.
He misspelled Odin. The story takes a real turn for the Norse in Act 3.
T’chk!
Well, I figured it’s not a spoiler to say “this name is used” and, when you encounter it, it’s just “ok, that’s the name”. Conversely it gives anyone in Act III a frame of reference on whether they want to read the spoiler or not
Yeah it’s hard to talk about this game because there are so many branching choices.
For instance, and please click the spoilers (Act 3) in order so that you can stop if you need to:
If you have Wyll in your party and you convince him to break his pact by sacrificing his father but then you side against Gortash by rescuing the Gondians and in the process successfully save his father, you get a quest to go wake up an ancient protector of the city which culminates in a massive reveal about the Emperor.
Also some cool loot.
I have a spoiler question about a fight in Act I: I beat the Hobgoblin with the help of my Ogre friends but I am pretty sure the Ogre threw him off the cliff as his body is gone. Did I break the story or am I just out the Sweet Loot he would have had on him?
The story should be fine, you just need him dead.
Hold ALT to see if he pops up as under someone/thing