Don't forget your legendary resistances (probably could have negated the dire wolves) and legendary actions. And remember, the given HP is just an average. You can always maximize the HP (max number on each dice) and even give the creature extra hp (because you're the DM)Last night we had a rather anti-climactic end for a big bad. Even though the fight would be memorable and humorous (trapping her under a folding boat and wailing on her), it wasn't much of a challenge.
Essentially the dragon lost Initiative, got pulled down by two summoned dire wolves, pinned to the ground, and was killed in less than two rounds. A monster that had a 70% chance of outright killing the entire party with a breath weapon, died before making a second attack and couldn't even move to reach a party member with an attack. It was a joke. The players (teenagers) were laughing around the table until they were snorting and falling out of their chairs.
The party is large but definitely not optimized (for example, the melee paladin has like a 12 Strength).
Here's the problem. I can't whittle down the group to fewer than 7 players. Doubling the number of monsters will slow down the game, not fit in the dungeon, and will also make boss fights too dangerous (in the case of the CR 10 dragon above, having 2 of them would have been too much).
What do I do? Would giving solo boss monsters two turns of Initiative take care of it?
That is a quick easy fix, but i might revise it to 1 additional legendary action/resistance per PC over 3.Just give monsters legendary actions and resistance equal to the Party's size-1, and max their HP out.
That generally is enough to make an interesting fight
3.5 style damage reduction & resistance is your friend as it will apply a flat reduction to every attack & spell by every player. That will allow you to push players to getting more diverse than GWM gwf great sword & fireball /scorching ray/repelling agonizing eldritch blast or whatever thru grouped up around. Unfortunately 5e won't offer you much help if you have more than a couple players & you have much more than a coupleLast night we had a rather anti-climactic end for a big bad. Even though the fight would be memorable and humorous (trapping her under a folding boat and wailing on her), it wasn't much of a challenge.
Essentially the dragon lost Initiative, got pulled down by two summoned dire wolves, pinned to the ground, and was killed in less than two rounds. A monster that had a 70% chance of outright killing the entire party with a breath weapon, died before making a second attack and couldn't even move to reach a party member with an attack. It was a joke. The players (teenagers) were laughing around the table until they were snorting and falling out of their chairs.
The party is large but definitely not optimized (for example, the melee paladin has like a 12 Strength).
Here's the problem. I can't whittle down the group to fewer than 7 players. Doubling the number of monsters will slow down the game, not fit in the dungeon, and will also make boss fights too dangerous (in the case of the CR 10 dragon above, having 2 of them would have been too much).
What do I do? Would giving solo boss monsters two turns of Initiative take care of it?
Without much information about your PCs (particularly there level) it is hard to say. Also, are you looking for a general guideline or guidelines for solo monsters? A couple of general suggestions I have seen, but have not used myself, is to modify a monster as follows:
You might need to tune those dials to your particular group.
- for each PC over 4 add 25% monster HP*
- for each PC over 4 add 25% monster damage or 1 attack*
- for each PC over 4 add +1 to all defenses
*Note: this can be by adding a monster(s) or increasing an individual monster
So your dragon would have 75% more HP, +3 to all defenses, and 3 additional attacks. This is assuming the CR 10 dragon was an appropriate challenge. I can tell that from the information provided

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.