This is not so hard. First though, you need to be in a game that does not allow the '15 minute day cheat' or the 'everything is in stasis until a fight happens cheat' or a 'knowledge roll/spell tells a player everything cheat' and other such cheats that allow a wizard to be over powerful.

1.Wear the wizard down. This is simple enough. You simply force the wizard into combat more then they can handle in a day. No matter what level the wizard is, they only have so many spells. And so many magic item uses and charges and such. So all you need do is push the wizard past that limit. Attack the wizard ten times in one day. For example have the first attack at 5 am, then the next at 7 am, the next at 9am and the next at 11 am and so on. That way the wizard uses up lots of magic. For example, the above three attacks alone would have used up four of the wizards stoneskin spells. Small, but deadly attacks by several groups can wear down a wizard. Summoned monsters work great here. This works even better with a 'nova' type wizard that burns out everything in every combat.

2.Trick the Wizard Going along with number one, you want the wizard to wear themselves down fast, and a great way to do that is to trick them into doing so. Illusions, polymorph and disguises can make a wizard think they are facing different or more powerful foes, and then use up and waste more and powerful magic. An easy example is dress a bunch of wild elves up as drow to get a wizard to use up all his spell resistance by passing stuff. You can also do things like disguise the red dragon as a white one, and let the wizard waste his uber fireballs on it. And again this works great on nova type wizards.

3.Protective Items Simple enough, when you go to fight the wizard protect your troops. There are tons of mundane and magical protections. Anything that can keep even a mook aline for one more round is more then worth it. Protection from energy can keep a foe alive a couple more rounds. And at the high end, you can fill in holes in a creatures defense. Giving a white dragon a ring of fire resistance, for example. This works great vs 'target weakness' type wizards that go crazy over finding a targets weakness and then taking advantage of it.

4.Surprise Attack Don't walk onto a battle field and stand across from each other and wait for the 'fight' all Mortal Combat style. Attack the wizard when they are not ready, when they are asleep or eating or relaxing. You can even do the trick of waiting until the wizard is already in combat with someone else, then attack too.

5.Take out the Wizards support Steal or destroy his spellbooks, destroy his home, kill his familiar or any other creatures or friends or allies. Steal or destroy all of his magic items. This can work out nicely with the wear down attacks as you can have dozens of creatures either steal or destroy the wizards items. Sunder and disarm can work great against a wizard and they often can't do much to resist the attack forms.

6.Enclose the Wizard Wizards work best with open spaces. Lots of spells need room. So simply maneuvering the wizard into a building or a dungeon cuts down on the wizards possible actions. The wizard can't cast a fireball in a 10x10 room without hitting themselves. The 'murder maze' also works good here, where you have foes behind walls or such that can attack the wizard. Also here you can grapple the wizard and tons of creatures can do that. Also plenty of terrain can hinder the wizard. And even tons of mundane attacks like webs or glue or ropes can stop a wizard.

7.Use the Law If the wizard interacts with any civilization, you might be able to use the law against them. Simply have or arrange for the local paladin to arrest the wizard. The crime could be real or fake, it does not matter. Most lawful wizards will allow themselves to be arrested as they 'believe in the system' and even an evil wizard might play along for social or political gains. Then once the wizard is in a cell, with no magic items or such, they are a much easier target for you.

8.The round-a-bout attack Use poison or anything else harmful to weaken the wizard before you attack. If the wizard is mortal, they will need to eat and drink, and it's not that hard to poison that. You can even do a whole scan just to get the wizard to a dinner just to poison them. And even if the wizard does detect poison on everything, you can do the simple mundane trick of poisoning everything. And the wizard might think it's a false positive. And you have the social trick: say the wizard is at the barons dinner and discovers his food is poisoned. The baron thinks that is crazy as the food was made by his best chief, so the wizard is thought of as crazy, and might have to eat the poison to keep the baron happy.

9.Target the Mortality And often forgotten about type of attack. Mortal wizards need things such as clean air to breathe, so attack that. For example, putting the wizard in a room full of smoke or sleep gas. The wizard may have lots of defenses vs attacks, but not much to let them breathe. You can do the same thing with filling a room full of water, or even just darkness(even just normal darkness). A wizard tricked into a underground poll of water in the dark can be in real trouble.

10.The Magic Attack Anti-magic is the obvious thing. As are mind effecting spells like feebelmind.


Now the thing is that a wizard could prepare an escape from any of the above. But your plan has two parts. 1) The wizard is 'not ready', so they are not walking around with a full set of 'adventuring gear and spells' and 2)The wizard can only escape so many times a day. You can set up five traps for a wizard before noon. Each time the wizard just laughs and teleports away. But then you keep after him....and by 5pm or so....the wizard will run out of teleport spells.