Though the distinction isn't hard-and-fast, components in this section are less concerned with improving the intelligence of creatures, more concerned with increasing their abilities and numbers. (Though hopefully, creatures remain intelligent and changes remain fairly low-key.) All components in this section are for TUTU/BGT/BGEE installs.
The doppelgangers in chapter 5 and later are by and large nothing like powerful enough to be an interesting challenge to a Tutu party at that level. This component (which has been overhauled for version 22) improves them mostly by systematising up, so that all ordinary Dopplegangers you meet are as powerful as the toughest ordinary Dopplegangers, and similarly for Greater Dopplegangers. It also increases the power and resources of the doppleganger assassins you meet late in chapter 7, giving them access to some spellcasting power.
Tougher Black Talons and Iron Throne guards
This component upgrades the Black Talon Elite and (most of) the Iron Throne mercenaries to L5 fighters. This doesn't have that much effect on the Black Talons (though they are now immune to Sleep); it's quite a substantial boost for some of the Iron Throne flunkies.
Improved deployment for parties of assassins
Two groups of assassins (one made up mostly of dwarves and gnomes, one made up entirely of amazons) hang out in the vicinity of Gullykin. This component removes them from there and makes them proactively hunt the party down instead - they'll show up at random times in chapter 3 once the main character hits third level.
As of version 24, the assassins spawn in the usual random-encounter areas on TUTU and BGEE games, and on BGT games with BGSpawns or BGT-Tweaks spawns. (The old behaviour is fun, but a repeated source of bug reports!) If you want to hold on to the old version, you can force it via the ini file.
Dark-Side-based kobold upgrade
This component substantially increases the number of kobolds met, and adds some tougher "Guards" and "Chieftains" - the Nashkel Mine becomes less of a walkover, especially if "Better calls for help" is also being used.
As the name suggests, this component is substantially based on a small subcomponent of the old "Dark Side of the Sword Coast" mod for BG. I haven't been able to track anyone down from that mod to ask permission (I'm not really sure where to start) - it goes without saying that if the authors of that mod would like the component removed I'd be happy to oblige.
Warning: this is, surprisingly to me, one of the more controversial components, as it's really a fairly sharp increase in difficulty. If your usual play-style is to go to the Nashkel Mines at first level, you may find it tediously difficult (both because you're too low-level to cope with the kobolds, and because you haven't had a chance to get used to SCS).
Relocated bounty hunters
In the original game, a tough group of bounty hunters are waiting pointlessly in a locked building in the Docks, with no explanation as to why. This small component moves them to somewhere more interesting - see here to find out where, if you want to spoil the suspense.
This component improves two of the tougher monsters in Ulcaster: Icharyd and the Vampiric Wolf. Both are pretty straightforward opponents in Tutu (more so than I remember from the original BG) and this component gives them a fighting chance. Both gain a few more hit points and some special powers (the Vampiric Wolf's powers are specific to the one in the ruins, they don't apply to all vampiric wolves).
Improved Balduran's Isle (requires TotSC or BGT)
This component makes a number of changes to the "Balduran's Isle" component of Tales of the Sword Coast. A couple of the main fights are made more interesting and the dialogue with Kaishas and Mendas is substantially altered. It is now possible to seek a significantly less bloody resolution to the island voyage. (see the readme for details)
Improved Durlag's Tower (requires TotSC or BGT)
This component improves the tactical challenge of a number of the key battles in Durlag's Tower. It is designed to be used with the "Smarter Mages" and "Smarter Priests" components, though it's playable without them. (see the readme for details)
At least one of these battles is now actually quite hard, though still perfectly doable by a seventh-eighth level party.
Improved Demon Cultists (requires TotSC or BGT)
This component ups the capabilities of the demon cultists you meet in TotSC. (see the readme for details) It's also pretty difficult for a party that isn't already 7th-8th level - be warned.
Improved Cloakwood druids
The druids of the cloakwood, even with improved scripting, are a pushover for a well-played party. This component increases their levels slightly and gives each a couple of low-level acolytes.
This component slightly increases Bassilus's level; it also makes his undead flunkies die off a little less quickly even if you say the right thing to him.
Improved Drasus party
This component upgrades the group of mercenaries you meet in chapter 4 guarding the Cloakwood mines: each gains a couple of levels.
Improved Red Wizards
This component adds three levels to each of the Red Wizards of Thay you can meet in the Wood of Sharp Teeth.
Improved Undercity assassins
This component enhances the (optional) final group of assassins you meet - each gains about three levels.
Tougher end-of-chapter battles
These components (there are four of them) improve the strength and numbers of the opposition in the end battles in chapters 2-5 - they are "upgraded" rather than massively overhauled, so they still aren't ridiculously hard. (There isn't currently a version for chapter 6 - I was dissatisfied with my previous one but haven't had a chance to put something new together.)
Improved final battle (requires TotSC or BGT)
By the end of the Tutu version of TotSC, the final battle of BG isn't much of a challenge. This component tries to change that and provide a worthier finale to the adventure. It turns out that Sarevok didn't just flee to the Temple of Bhaal because it looked pretty - he has other surprises... (see the readme for details).
Improved miscellaneous encounters
This component mildly increases the difficulty of a half-dozen or so battles scattered through the game, usually by increasing opponents' levels by one or two. It creates "divertingly" difficult fights rather than really stiff challenges. See (see the readme for details) for the specific battles if you want to spoil the surprise!