D&D monster tactics are hugely important in game play, without opponents that are as capable and tactical as the players the game suffers and the monsters you have spent so long crafting become dull and two dimensional punch bags.
Something even worse happens however - the players have a tendency to morph into entitled frat boys/girls who simply wander round the fantasy world you've lovingly created annihilating everything they encounter. The need for caution, avoiding certain threats, for problem solving instead of slaying, for subtlty, diplomacy and cunning all go out of the window because your players are invincible.
This is a recipe for dull and it also makes for bored, frustrated players who imagined being unstoppable might be fun, but when they actually find a world with no challenge in it, learn that it is utterly tedious.
Fear not though, for there are countless ways to knock those strutting popinjays down a peg or two (remember, you're being cruel to be kind here), and to give them the challenge of their character's lives.
If you use some of the strategies below, the game doesn't have to become a power-up arms race either, where you have to use ever more powerful Beholders, Dragons etc in order to challenge your players. If you use the strategies suggested, then low or mid challenge rating monsters can suddenly punch above their weight significantly.
Players who have had it too easy for too long might moan a bit but in the end you'll have far more engaging and gripping games. This is ultimately what we're in gaming for, that nail biting moment when we watch every dice roll and wait to see if the players have triumphed. Nobody goes to see a movie where the hero's ultimate triumph is a foregone conclusion, instead we watch movies where the hero has to expend every last drop of sweat to beat the villain. All of a sudden we really get to know the hero by finding out exactly what they're made of.
This is what most players are trying to achieve with their own heroes, to learn all about them by testing them and challenging them. This can happen in a number of ways, such as by giving the character difficult tasks to complete, by forcing the character to confront moral dilemmas or difficult choices, or by putting the character in dangerous or stressful situations. By pushing their characters to their limits, players can learn more about what their characters are capable of, what they are willing to do, and what they believe in.
All of this is facilitated through smarter monsters that are just as determined to survive as the players are.
Flanking: Monsters might try to position themselves on opposite sides of a player character (PC), taking advantage of the fact that characters have a harder time defending against attacks from multiple directions.
Example: The PCs are fighting a group of goblins in a narrow tunnel. One of the goblins positions itself on one side of the tunnel, while another goblin positions itself on the other side. The goblins then attack the PCs from both sides at once, taking advantage of the fact that the PCs have a harder time defending against attacks coming from two directions at once.
The goblins are hoping that this tactic will allow them to deal more damage to the PCs, since the PCs will be unable to concentrate their defenses on one side or the other. The goblins are also hoping that this tactic will create confusion and chaos among the PCs, making it harder for them to coordinate their attacks and defenses.
Overall, the flanking tactic is a common one used by monsters in D&D, especially in situations where the monsters have a numerical advantage or where the terrain or layout of the battlefield gives them an advantage. By positioning themselves on opposite sides of the PCs, monsters can create a pincer attack that can be difficult for the PCs to defend against.
Crowd control: Monsters might use abilities that incapacitate or hinder the movement of PCs, such as stunning them or entangling them in vines. This can make it easier for the monster to pick off individual PCs or focus its attacks on a smaller number of targets.
Example: The PCs are exploring a dark and treacherous dungeon, when they suddenly come across a group of giant spiders. As the spiders approach, one of them rears up on its hind legs and begins to spin a web, aiming to entangle and immobilize the PCs. The other spiders take advantage of the distraction to scuttle forward and try to bite and poison the trapped PCs.
In this example, the giant spider is using its web-spinning ability as a form of crowd control, aiming to hinder the movement and actions of the PCs. By entangling the PCs, the spider makes it easier for itself and its companions to attack the PCs without having to worry about being flanked or avoided. The spider is also using its poison ability to try to weaken the PCs, further increasing its chances of success in the fight.
Ganging up: Monsters might try to surround and overwhelm PCs by attacking in large numbers. This can be especially effective if the PCs are already weakened or otherwise disadvantaged.
Example: The party of player characters (PCs) has been battling a group of Orcs for what seems like hours. The PCs are tired and their spells are running low, while the Orcs seem to be coming at them from all sides. Just when the PCs think they have the upper hand, a Orc chieftain appears at the head of a large group of reinforcements. The chieftain calls out to the other Orcs , rallying them to attack the PCs with renewed ferocity.
The PCs try to hold their ground, but the goblins are too many, and they start to be surrounded. The PCs are forced to retreat, but the goblins are right on their heels, attacking them from all sides. The PCs are already weakened, and they struggle to fend off the Orcs' relentless attacks. It seems like they will be overwhelmed at any moment.
In this example, the goblins are trying to surround and overwhelm the PCs by attacking in large numbers. The fact that the PCs are already weakened makes it easier for the Orcs to succeed in their attack, as the PCs are less able to defend themselves. The Orc chieftain's leadership also plays a role in coordinating the Orcs' attack and keeping them motivated.
Hit and run: Monsters might try to attack and then retreat, either to regroup or to lure the PCs into a trap. This can be especially effective if the monster has a high movement speed or can otherwise move quickly and easily through the terrain.
Example: The PCs are exploring an ancient temple filled with traps and puzzles, when they come across a group of giant spiders. As soon as the PCs enter the room, the spiders attack, biting and poisoning several of the PCs. However, instead of continuing to fight, the spiders quickly retreat back into their webs, disappearing from sight.
The PCs are left to deal with the poison and their injuries, wondering if the spiders will return. As they continue to explore the temple, they notice that the spiders are always one step ahead of them, attacking and then retreating before the PCs can get a good shot at them. The spiders seem to be luring the PCs deeper into the temple, but the PCs are not sure why.
As it turns out, the spiders were being controlled by a powerful necromancer who had taken up residence in the temple. The necromancer was using the spiders to lure the PCs into a trap, hoping to capture them and use their bodies as experiments for her dark magic. However, thanks to their quick reflexes and clever thinking, the PCs were able to outsmart the necromancer and defeat her, freeing the spiders from her control in the process.
Ambush: Monsters might try to set up a surprise attack, either by hiding and waiting for the PCs to come to them or by using stealth to get close to the PCs before attacking. This can be especially effective if the monster has a significant advantage in terms of numbers or power.
Example: The party is exploring a dark and abandoned castle when they hear a loud growl coming from behind a closed door. They decide to investigate and slowly push open the door, revealing a room filled with shadows and rubble.
As they cautiously step inside, they suddenly hear a series of loud thuds and five ghouls drop from the ceiling, landing in front of them. The spiders had been hiding in the rafters, waiting for the party to come close enough for them to attack. The ghouls have the element of surprise and are able to strike first, taking the party off guard and giving them a significant advantage in the ensuing battle.