You learn quickly DMing that fight difficulty is determined more by action economy on either side than it is solely by HP and DPS. Generally the side with more actions per turn does better, so putting the party in a technically "Deadly" encounter against a single target, they still might just breeze through it.
When engineering really difficult encounters, try experimenting with different types of enemies in the encounter, maybe beats with complimentary fighting styles, or even just give your dragon some squishy minions to deal with before they get out of hand.
If you really do wanna go the single target BBEG route, think about tweaking the monster, either higher AC or HP, or give them extra actions /abilities. You can also play around with the terrain--maybe you're fighting on an erupting volcano and the lava is causing the accessible parts of the battlefield to change constantly so you can't always be in a position to attack the boss.
Basically, getting to the higher tiers of play just means that you need to get more creative with presenting challenges to players, and just throwing a dragon their way rarely cuts it.
You learn quickly DMing that fight difficulty is determined more by action economy on either side than it is solely by HP and DPS. Generally the side with more actions per turn does better, so putting the party in a technically "Deadly" encounter against a single target, they still might just breeze through it.
When engineering really difficult encounters, try experimenting with different types of enemies in the encounter, maybe beats with complimentary fighting styles, or even just give your dragon some squishy minions to deal with before they get out of hand.
If you really do wanna go the single target BBEG route, think about tweaking the monster, either higher AC or HP, or give them extra actions /abilities. You can also play around with the terrain--maybe you're fighting on an erupting volcano and the lava is causing the accessible parts of the battlefield to change constantly so you can't always be in a position to attack the boss.
Basically, getting to the higher tiers of play just means that you need to get more creative with presenting challenges to players, and just throwing a dragon their way rarely cuts it.
(Also Mordenkainen's Tome of Foes has a lot of high-tier monsters designed for that kind of thing)