Do external, non-innate methods exist in Faerûn circa 1489 DR to situationally alter the efficacy of spellcasting?

Question

Prior to D&D5e, Forgotten Realms lore included situational methods and circumstances that could change the way spells and spellcasting worked. For example, the 1e product Volos' Guide to All Things Magical includes a lengthy section on the use of various materials as special spell components. Using, say, a star sapphire in the casting of globe of invulnerability would increase level of spells warded off by the globe (see VGtATM p. 51). On the other hand, consuming the herb spellbane detailed in the 2e product Volo's Guide to Cormyr would entirely suppress spellcasting ability for a period of time (VGtC p. 110).

Faerûn has changed a lot across editions, however, and nowhere is that more true than in the way magic and spells work. Maybe those old methods of amplifying or weakening spells and spellcasting are still effective, or maybe they aren't. Is there any lore either way in 5e-era publications, i.e., in the Realms as they are post-Second Sundering, circa 1489 DR? Are there any other, different but comparable methods available?

To be clear, I'm interested in methods that are ephemeral and external to the caster and/or target -- not innate abilities, learned skills, divine gifts, etc. Magic items are acceptable to the extent they actually engage with lore specific to Forgotten Realms. For example, a generic 5e wand of the war mage technically alters spellcasting ability, but not in any way that depends on the spellcaster being in Faerûn. Special substances (magical or otherwise) showing up in Forgotten Realms lore are fair game. Even Faerûnian locations with special properties that change the way spells function would fit the bill.

Answer 1

Here are some effects that alter the outcome of spells from adventures set in the forgotten realms that I found:

From Baldur's Gate: Descent into Avernus:

With your permission, a character who casts the find familiar spell can henceforth choose to conjure an abyssal chicken instead of a raven.(pg. 96)

From Waterdeep: Dungeon of the Mad Mage:

With years of study, any creature that can cast the symbol spell can learn an elder rune and add it to the selection of symbols that can be created with the spell. (pg. 12)

Any spell cast within 30 feet of the arch automatically triggers a wild magic surge, the effect of which is determined by rolling percentile dice and consulting the Wild Magic Surge table in the "Sorcerer" section in chapter 3 of the Player's Handbook. (pg. 172)

A permanent enchantment in this chamber grants any creature in the area advantage on saving throws against being charmed, and causes the levitate and detect thoughts spells to automatically fail when cast. (pg. 213)

From Tomb of Annihilation:

Casting teleport or misty step moves the caster sideways instead of up to the next level. Bypassing the tests by any means is flat-out impossible. It might help to think of the whole situation as a fairy tale; it doesn't need to make sense, because the magic of Orolunga is on a mythic scale that overpowers the ability of any mortal. (pg. 80)

Many spells have altered effects when cast in the Tomb of the Nine Gods, including spells cast from magic items or artifacts, and class abilities that duplicate the effects of spells. Acererak's magic and the magic of the amulet of the black skull (see appendix C) are unaffected. (pg. 128)

Answer 2

There are several environmental effects in the Sword Coast Adventurer's Guide

The section is an inset on page 19 of the SCAG, under the Magic in the Realms heading and includes the following (none of which are new, I think, but this at least is confirmation they still exist in 5e):

• Dead Magic. In rare areas of dead magic, the Weave is absent. Not only do spells and magic items cease to function, but even the supernatural abilities of creatures that are innately tied to the Weave might fail as the knot of the Weave they carry with them unravels.

There also is an abandoned wizard's tower with a dead magic zone in Waterdeep: Dragon Heist.

• Wild Magic. In an area of wild magic , the Weave becomes "tangled," spontaneously forming its own constructs and resulting magic. It also tends to twist the constructs of the Weave created by spellcasting, causing unexpected results.

I am not aware of any consumable items that would influence spellcasting (make it cheaper, extend durations, etc.) if consumed before or during casting or used as a material component. The only thing remotely similar I know of (which would be available in the Forgotten Realms, but is not specific to them) is the candle of invocation, which partially reads:

The candle's magic is activated when the candle is lit, which requires an action. After burning for 4 hours, the candle is destroyed. You can snuff it out early for use at a later time. Deduct the time it burned in increments of 1 minute from the candle's total burn time.
(...) a cleric or druid in the light whose alignment matches the candle's can cast 1st- level spells he or she has prepared without expending spell slots, though the spell's effect is as if cast with a 1st-level slot.