Misdirection

Sometimes, a bit of misdirection can add a lot of interest to an encounter, especially against offense-heavy groups. Rather than amping up the opposition to match the PCs' firepower and creating opponents whose own offenses are too powerful for the PCs' defenses, consider a little sleight of hand. For instance, a villain might have a hologram or disguised robotic double with just enough durability to take a few hits while the true villain is hiding nearby, ready to emerge and attack. Illusion spells and holograms can allow a foe to attack from a safer position, and possession grants the foe a disposable body unless the PCs brought along spirit blast or similar magic. Sometimes you can even hide the villain in plain sight, or the villain dies the first time the PCs defeat them in combat. Some might escape, perhaps through teleportation, misdirection, or with other ploys. When a villain escapes and lives to fight the PCs again another day, it's good to have that foe learn from their past failures. In their next encounter with the PCs, give them additional minions, spells, or other defenses designed to counteract the strategies the PCs used against them previously. Even if the villain doesn't escape, they might have other tricks up their sleeves, such as rising again to oppose the PCs. They could well return later in the adventure—or they might come back immediately for a second battle, so long as there's a proper justification for doing so. For example, defeating an otherworldly villain's outer shell might reveal its terrible true form, or an evil witchwarper from another timeline might have a more powerful alternate self who already defeated the PCs once and is wise to their tricks the next time he faces them!