The Main points of interest are:
Ability score bonuses are derived from the OSE equivalents in general. So 18 gets you +3 instead of +4. And no bonuses until 13.
Dumped THAC0 and BAB for the 5e proficiency system. Each class receives a certain number of Weapon Proficiencies similar to 2E. If the PC is proficient in a weapon, they can add their prof bonus plus ability mod, otherwise just straight ability mod with said weapon. Fighters, and only fighters, can specialize in a weapon for two slots which gives them +1/+2 and a faster attack rate.
PCs need to take proficiency in two ability scores - determined by class choice - and on those checks they receive their level dependent prof bonus. This takes the place of ‘skills’ in 5e or non weapon proficiencies in 2E.
Saves are just ability checks. The same two scores they take proficiency in they are proficient in those saves.
Using slightly modified class/race abilities from AD&D 2E PHB. The mods are to fit into the proficiency system from 5e in general. The Thief is the biggest deviation in the classes IMO where in this hack they get an extra bonus to their proficient ability (skills) checks equal to their level to simulate their specialized skills. The Magic-user is slightly beefed up with one extra spell slot at each level, and a couple cool abilities at the higher levels in this 10 level system. HP is rolled at every level, no averages, etc. The HD are mix mashed, d6, d8, or d10. The human get’s some interesting options as far as races go. They can choose to take a +1/-1 to ability scores of their choice, receive 5% xt xp at default, and they get an ‘heirloom’ to start out, which could be just about anything (minor magic item) to start. Added a Beastman race as well.
Using class restrictions and multi-class rules from 2E for the demi-humans, but no level limits. Max level is 10 anyhow. Humans can multi-class (no dual classing) as well without restrictions* like the demi-humans have.
*Some universal restrictions apply, for example, no multi-classing Thieves and Paladins, no picking 2 warrior classes or Thief/Bard combos. But a Ranger/Magic-User is acceptable, as is a Cleric/Paladin.
Modified initiative system as well. AC posted here: Rethinking Initiative: Phases, not Turns and I loved the idea, so I took some of that into my own thinking. In essence, each round is a number of phases, and init is side based. Winning side goes first in each phase throughout the round. Might seem slower at first, and it very well may be in practice, but I want to test it out first before changing it up.
Spells could theoretically be anything you want, but I included the OSE SRD spells in this pdf. Equipment is the same, could be whatever you wish, but included the OSE SRD for sake of ease for now.
Morale is used as are Reaction rolls for both NPCs and Monsters. Hirelings/Henchmen mentioned, pricing and other rules mostly left up to the GM.
For myself, I am assuming the use of OSE/2E monster stat blocks as 5e monsters would most likely decimate characters in this game.
My goal was to put on paper my idea of nearly perfect DnD, using the bits and pieces from all the editions I love. 5e’s mechanics in a lot of ways are fantastic for ease of play, but the overall power level of classes and the monsters gets very unwieldy passed lvl 5 or 6. This changes that, and adds in some greatness from the older editions that I loved.
Let me know what you think!