D&D 5E Player character lv 10 wizard who is also smart player how to challenge?

[Nightbeat84]

I do not want to go into detail about whether or if you single out a wizard character, I believe you just ask for things that could be challenging for this character class and that is a fair question:
Counter spell, but do not overdo it.
Enemy spell casters can have shield also (think magic missile)
Also Dispel magic by enemy casters on enemy mobs which have been debuffed or restrained by the PC wizard.
More mundane (in a very fair way I think, I did it like that lately): Assume group of enemy mooks some melee some ranged and some commander. As soon as the PC wizard shows his danger e.g. casts a fireball decimating the enemy number, the commander reacts and orders his ranged soldiers to focus fire on the PC wizard. in that way he is allowed to shine but it has a price attached to it.

Some odd stuff: wild magic and magic dead zones (these were a nice gimmick coming up for FR in former editions, I do not know why this is not so popular anymore). Of course you need a justification for these to be there: For FR a former or damaged Mythal justifies the presence of these. For wild magic use any table also from former editions, or make up your own funny stuff like the caster farting butterflies, or a very cruel one (for some) changing gender.

I remember reading about the wild magic zones witch I think in some places can be instilled to have random effects I can justify. I have a few ideas on how to implement them, just need to make or find a roll chart that I like lol
Thanks for the great advice

 

[tommybahama]

One DM I played with simply announced the NPC was casting a spell without telling us what spell he was casting. We had to decide to cast Counterspell without knowing what was being cast. Have that work both ways for your player and NPCs. Neither side knows in advance if the next spell is a cantrip or high level spell when they are deciding to cast Counterspell. It would add an additional layer of tactics to spell casting which could be fun or at least more interesting.

I can see the fighter in the group yell out, "Do the fireball! Do the fireball!" so that the enemy NPC spellcaster immediately Counterspells the next spell cast, not realizing that the player spellcaster always starts out by casting something like Minor Illusion instead.

 

[Flamestrike]

Yup seems to be more about smaller and many more encounters then a few big ones, as the players level I'm thinking that they can handle more little ones maybe not all of the encounters due to IRL time restraints for that game session. Stretch the in game time over more sessions.

Next adventure, try this:

The PCs get wind somehow of an evil cult threatening the town (or some BBEG of your choice). The BBEG has captured (some NPCs important to the PCs?) and intends on sacrificing them at midnight, as part of a ritual to summon a potent (Demon Lord?).

The PCs must penetrate the dungeon and stop the ritual (and save their friends), before its too late.

Use the above as both your 'hook' to get the PCs involved, and also as the framing device for the adventure. Ensure the PCs roughly know that they're on the clock.

From there, simply map out the dungeon, and stat up half a dozen or so encounters for them to deal with. Place a few areas where a Short rest is possible, in natural breaks in the adventure or story.

 

[Coroc]

I remember reading about the wild magic zones witch I think in some places can be instilled to have random effects I can justify. I have a few ideas on how to implement them, just need to make or find a roll chart that I like lol
Thanks for the great advice

If your players are not familiar with this gimmick you absolutely have to use it somewhere, it is hilarious for the table. Good tables are the wildmagic sorcerer table in 5e and in the 2e tome of magic (you might have to convert some of the effects to 5e) to name the most readily available.
Some 2e adventures also contained their own wild magic tables, but I cannot remember which ones.
Do not forget that the wild magic also applies to other arcane magic classes (EK, Sorc, Bard)