I'm porting some content from 3.5e to 5e, and I've come to a part that has a group of npc paladins doing mounted combat with lances. Checking the 5e rules for lances, I don't see anything about doing double damage on a charge. Are lances just not any good in 5e?
Is there a reasonable 5e equivalent of mounted lancers that I can use for these paladins, or do I have to houserule everything?
The benefits of a lance are built into its properties:
If your DM allows it** lances synergize well with the Charger feat, which grants bonuses for charging and may make the lance feel more 3.5e-ish.
Note that the mounted/reach combo is quite powerful if leveraged well. On a proper mount you can attack something mid-move, and then finish your move a fair distance away without incurring (most) attacks of opportunity from your target.
* Statistically only 2d6 is superior to 1d12
** It has been pointed out that the Charger feat is not activated when a mount uses dash according to a tweet by Jeremy Crawford
Since you speak of NPC lancers, I'm going to assume you need "monsters", or at least adversaries, not player options. In which case, the added power of a monster wielding a Lance or other such weapon is baked into the creature stats, not the general player rules.
Check for example the Centaur, Unicorn or Minotaur.
They all have a power called Charge which works roughly like this:
If the unicorn moves at least 20 feet straight toward a target and then hits it with a horn attack on the same turn, the target takes an extra 9 (2d8) piercing damage. If the target is a creature, it must succeed on a DC 15 Strength saving throw or be knocked prone.
If you're looking for mounted NPC Paladins for your players to do battle with, you should probably give them a power of the same type to represent their mounted lancing.
Out of the Abyss features a group of Duergar that are mounted combatants called Kavalrachni.
They're pretty easy to adapt to any race that you want because they only have this unique ability that sets them apart from any old Duergar:
Cavalry Training. When the duergar hits a target with a melee attack while mounted on a female steeder, the steeder can make a melee attack against the same target as a reaction.
This is perfect for the "Lancer" feel, as it synergizes surprisingly well while the creature is mounted, here's why:
Normally, a controlled mount has only a limited number of actions, according to PHB 198:
... [a mount] moves as you direct it, and it has only three action options: Dash, Disengage, and Dodge.
With Cavalry Training, a rider can order its mount to make one attack as a reaction if the rider hits with his attack first, essentially breaking the above rule.
The above can be further amplified if the mount has Trampling Charge, like a Warhorse (MM 340):
Trampling Charge. If the horse moves at least 20 feet straight toward a creature and then hits it with a hooves attack on the same turn, the target must succeed on a DC 14 Strength saving throw or be knocked prone. If the target is prone, the horse can make another attack with its hooves against it as a bonus action.
Because a mount and rider share their turns, the reactionary attack from Cavalry Training can activate Trampling Charge, essentially allowing a 3-hit combo (Lance, Hooves, Hooves).
CR Change. Out of the Abyss says that a Kavalrachni has the same stats as a Duergar but with this trait, its CR increases by 1. By my estimates, and looking at similar creature abilities, I would add the potential damage from the mount's highest-damage melee attack to the rider's DPR.
Is this overpowered? Not really. So many things have to go right for the rider and mount:
At any point in that process one of those aren't fulfilled, this glorious combo cannot be attained. If it does, though, it's pretty devastating... Kind of like getting hit by couched lance, and a charging warhorse.
