Limitations of Illusory Reality

Illusory Reality states:

By 14th level, you have learned the secret of weaving shadow magic into your illusions to give them a semireality. When you cast an illusion spell of 1st level or higher, you can choose one inanimate, nonmagical object that is part of the illusion and make that object real. You can do this on your turn as a bonus action while the spell is ongoing. The object remains real for 1 minute. For example, you can create an illusion of a bridge over a chasm and then make it real long enough for your allies to cross.

The object can't deal damage or otherwise directly harm anyone.

In short, the Wizard can manifest an object which:

• is real, inanimate, and non-magical
• cannot directly harm anyone
• disappears after one minute

Moreover, because the object manifested by the wizard is real, it follows all the normal rules for object detailed in the DMG's Objects section (p. 246-247). In particular:

For the purpose of these rules, an object is a discrete, inanimate item like a window, door, sword, book, table, chair, or stone, not a building or a vehicle that is composed of many other objects.

This limits the complexity of what can be considered an object and excludes indiscrete things like gasses, liquids, and holes.

Finally, the Wizard cannot use Illusory Reality to disappear or transform a preexisting objects and the Wizard has no special control over the manifested object.

Curtail Illusory Reality by

Preventing its use

Anything that prevents the Wizard from casting spells, also shuts down Illusory Reality because the Wizard needs to cast an Illusion spell to create an object. Some relatively common examples which fall in this category and which specifically hinder casters are silêncio e contra-feitiço.

Dissipar magia can also dispel an illusion and prevent the use of Illusory Reality, but do note that dispelling the illusion after the Wizard has manifested an object will not cause the object to disappear.

Rolling for uncertain outcomes

The Wizard can manifest an object without fail within the limits of Illusory Reality, but that does not mean that the Wizard always achieves the desired outcome.

The DM should not try to undermine the player, but when an outcome is uncertain, the DM can (and often should) call for a roll, be it an ability check or a save. Referencing traps and spells can help to understand when a roll is adequate.

For example, the Wizard can create an adamantine dome using Illusory Reality, but whether that dome will capture a creature as it manifests is uncertain. The DM could rule that the creature is just captured like gaiola de força or call for a save like muro de pedra. Both are equally valid, though I would urge for a consistent choice on the DM's part.

Destroying the object

Once the object exists, the characters can destroy it. The Objects section mentioned previously offers some guidelines:

When characters need to saw through ropes, shatter a window, or smash a vampire's coffin, the only hard and fast rule is this: given enough time and the right tools, characters can destroy any destructible object. Use common sense when determining a character's success at damaging an object. Can a fighter cut through a section of a stone wall with a sword? No, the sword is likely to break before the wall does.

Of course, the objects only exists for one minute, so a thick wall or boulder is probably going to survive that minute no matter what the DM throws at it, but that is not the case for all objects.

The same section of the DMG includes tables to determine the AC and HP of objects. For example, an adamantine cart is a large object with 23 AC and 27 HP. Enemies suitable for a party of level 14 characters can easily destroy something like that in one round.

I recommend reading the whole Objects section in preparation for a Wizard with Illusory Reality.

When you cast an illusion spell of 1st level or higher, you can choose one inanimate, nonmagical object that is part of the illusion and make that object real. You can do this on your turn as a bonus action while the spell is ongoing. The object remains real for 1 minute...The object can't deal damage or otherwise directly harm anyone.

From the definition of Illusory Reality, I read this as saying it can create new objects -- não take away existing ones, like a floor, nor create weights to fall on people (as that would deal damage and harm people). This use of Illusory Reality seems against RAW.

Your specific descriptions of the Wizard's use of Realidade Ilusória is not supported by RAW

By 14th level, you have learned the secret of weaving shadow magic into your illusions to give them a semireality. When you cast an illusion spell of 1st level or higher, you can choose one inanimate, nonmagical object that is part of the illusion and make that object real. You can do this on your turn as a bonus action while the spell is ongoing. The object remains real for 1 minute. For example, you can create an illusion of a bridge over a chasm and then make it real long enough for your allies to cross.

—Illusory Reality, Player's Handbook, pg. 118

Realidade Ilusória allows a wizard to create an illusion, and then make an object in that illusion real; it doesn't permit them to take an object that already exists and make it "fake" for the duration. So the following kinds of tactics would not be permissible:

• Making an illusion of a hole in the floor and then making the floor not exist in the area of the hole to drop creatures/objects resting on the floor
• Turning a large boulder/whatever illusory so it drops through a floor, then ending the illusion to turn it real again

However, it is possible to get very near to these tactics in a fully rules-supported manner

For example, the following tactics seria be perfectly legal:

• Creating an illusion of a stone floor across a chasm, making it real, chasing an opponent onto the floor, and waiting for the object to become an illusion again to drop them to their deaths
• Creating an illusion of a net or bowl or whatever to hold up a heavy object, placing the heavy object on that [illusory] support, waiting until an opponent is under it, and then waiting for the illusion to end to drop the object onto the opponent for massive damage

So while this player is bending the rules a bit, it wouldn't be terribly difficult for them to be nearly as effective as they've been by just tweaking their methodology and planning.

Illusory Reality is a 14th level Wizard feature. Any character who gains access to this feature already has access to extremely powerful spells, being a spellcaster with 6th and 7th level spell slots. There's probably a lot of ways they could cause similar havoc without needing to specifically abuse this feature. So while I understand your trepidation, the reality is that these kinds of uses of Realidade Ilusória is probably not their most powerful feature, their flouting of the rules notwithstanding.

Even if this interpretation of Realidade Ilusória worked (RAW), potential answers to the question are resistência to the effect and a tactical response to the effect.

Up front, this is a questionable use of Realidade Ilusória. It's not obviously permitted from the feature's description as written, and interpreting it in a way that allows these uses starts stepping on other spells and abilities as well as risking imbalance in the game. Those reasons alone are enough justification for the DM to prohibit these effects.

However, the character in question is level 14. That indicates some pretty spectacular abilities, and while the effects described in the question are striking they aren't necessarily too far off other things a level 14 Wizard could do.

For example, casting bola de fogo at it's lowest level (3) allows the Wizard to (potentially) do up to 8d6 damage, equivalent to 80 feet's worth of falling damage, to as many targets as fit in its 20 foot sphere of effect (easily 6 humanoid enemies). The spell's area of effect is similar to that of Imagem principal, which affects a 20 foot cube, and requires no setup or convenient layouts to create the 80 foot fall hazard. Upcasting it adds additional d6 to the damage. So even if the player is abusing Realidade Ilusória in particular, it's not necessarily granting their character outsize power.

At level 14, the game world should contain a huge number of cannon fodder opponents who can't meaningfully challenge the party and that the party can defeat with ease. For those enemies who need to provide a greater challenge, counters and resistances can make most of the difference.

Countering the Effects:

If the player is a powerful Illusionist, a creature which can more easily perceive illusions will frustrate any illusion-based trickery the player might come up with:

• Some creatures have high stats which can counter illusions
• Others have Truesight, and can immediately identify illusions for what they are
• Still more might have access to spells like Verdadeiro Ver, directly or via magic items, lair effects, or minions
• The traps described in the question take time to set up. Depending on when the PC sets up their traps, any of these might be enough to render them useless.

Enemies which don't have abilities allowing them to deal with the illusions directly can still develop estratégias to deal with an Illusionist. At level 14 the PC is probably at least moderately famous, and even if not famous in general a persistent enemy (or faction of enemies) will encounter the PC many times and observe how they do things.

It's not implausible for the antagonists to get better at dealing with this PC over time. Those enemies might develop tactical approaches to mitigate the danger:

• They could just spread out so that something like the vanishing floor can't affect so many of them at once
• They could send more enemies so that the vanishing floor won't be as decisive in the fight
• They could send waves of enemies, with the first as a "decoy", causing the PC to spring their trap to deal with the decoy force only to find themselves trapless for the "real" squad
• Sniper-type enemies might consider this PC a high-priority target, focusing fire on them to disrupt their concentration on the underlying Illusion spells or forcing them to spend more high-level spell slots to pull off these tricks
• Sequences of combat encounters (among other types of encounters) consume PC resources, including spell slots. Circumstances might make using spell slots in this way unappealing, or there may simply be too many combat encounters for uses of Realidade Ilusória to be an option in all of them

The DM can also impose some more arbitrary hard counters on these tactics, though if the player is creative this will always be a lagging solution. If the combat area is on the top of a 60 foot mound of solid stone, you've put a ceiling on how much falling damage can be inflicted with the vanishing floor trick. If the DM decides that dropping a heavy weight on someone is effectively an Attack, the player may have to roll a d20 to determine a hit, or the enemy might have a chance for a DEX to avoid the hazard.

tl; dr:

A high-level character is expected to have lots of options in battle, and to be able to deal a lot of damage to multiple enemies per combat turn. This is not abuse. Powerful characters are powerful. Abuse is more a matter of rendering challenges irrelevante em vez de beatable or mais fácil.

Whether RAW-allowed or not, DMs have tons of options to respond to player strategies, including but not limited to forbidding those which make the bulk of the game irrelevant.