Can I ask you for some advice? Heres my situation (first session is this Saturday):
I'm the DM. Been doing it 20 years but havent played 5e. I read the rules, but Most of the players will know the system better than me in the beginning. I have 1 veteran player, 2 intermediate, and 1 brand new player. Is class balance going to be an issue where the new player makes a vanilla PHB, and the more experienced players make something out of Tasha's? (Which I dont have either so that could be a surprise). I'm not going to restrict the characters even if I don't know the system. I've got enough DM experience to figure it out pretty quickly.
My two main questions would be:
1. What sort of quirks about 5e could trip up a DM new to the system?
2. How big of a gap is there between certain classes, and how big can the gap be between player skill?
There are some quirky rules regarding initiative rolls. Since rolling for initiative is a dexterity check, certain abilities that apply to ability checks such as bard: jack of all trades, and champion fighter: remarkable athlete, can enhance a players initiative roll. Super easy to overlook those.
Ability score rolls do not automatically fail on a natural 1. If your modifier is high enough to still pass the DC, you pass. Attack rolls still auto fail on 1s and auto hit on 20s.
Handing out inspiration about once per session is a fun way to give people an extra, oh shit button.
Relying on darkvision incurs disadvantage on visual perception checks. Counts as dim light and only see in shades of gray.
Being hidden from a target grants advantage, being unable to see a target grants disadvantage. One source of advantage cancels all forms of disadvantage and vice versa. Magical darkness is hard to see through even for normal darkvision. This almost always creates a scenario where everyone still rolls normally since no one can see their targets, but are simultaneously hidden from them. Warlocks devil sight, true vision and blind sight can overcome this granting advantage on attacks and disadvantage to attackers.
There are no "surprise" rounds per se. Beginning of any combat have everyone roll initiative. Proceed down the initiative list. Skip over any creatures or players you belive to be surprised by this combat occurring. That was the first round of combat.
Any creature that suspects combat may be possible in the near future, can't be surprised, like a Guard actively looking for danger. A guard who is sleepy or not paying attention however... Surprise only lasts for the first round of combat.
Stealth allows a creature to move quietly and to not draw attention to themselves. It does not grant invisibility. Trying to stealth through an open, well lit courtyard in direct line of sight of other creatures should be next to impossible and require a godlike roll (30+)
Invisibility makes a creature impossible to see without magical means, but does not make them silent. They can still trip, bump into things, sneeze ect.
For class balance:
OG beast master rangers had a tough time.
Paladins of any stripe are powerful, especially oath of vengeance and oath of the crown.
Spellcasters take a good understanding of which spells are useful and when to get the most out of them. A wizard that picks lack luster spells will have a much harder time shining.
Healing is... not usually the best use of an action mid combat unless someone is down, even then if you can dump more damage then they could you are probably better off just burning enemies down and then healing when there are only a few left/ out of combat.
Crowd control abilities and spells can completely shut down an encounter. They are the most powerful actions a player can take by a huge margin provided the enemy does not have immunity/ legendary saves.
Classes that get most or all of their resources back on short rests versus ones that need long rests are much better at handling lots of encounters per day.
Action economy is everything. A veteran player will plan out their character to have a solid option to use their action, bonus action, reaction and movement every turn.
Archery fighting style makes the sharpshooter feat much more consistent.
Any class / feat/ spell/ saving roll that allows a character to reduce damage by half that is not specifically granting resistance to a damage type can also apply the appropriate damage resistance to cut damage to 1/4.
Barbarians and fighters are still really solid. They don't have lots of tools but so long as they are able to close the gap they can dish out damage without too much micro management. Very durable characters.
Certain feats are incredibly strong and others are basically useless. Newer players might not be able to tell which ones grant the largest benefit.