#4e dnd

First, stop the constant escalation and management of modifiers by cutting out everything except for the basic ability score modifiers. No half-level bonus, no item enhancements, no feat bonuses, no power bonuses, no skill bonuses, no proficiency bonuses. No circumstantial or conditional or temporary modifiers of any kind. Just 1d20 plus ability mod, period. Reconstruct the weapon tables to eliminate traits like high-proficiency and versatile.

Then, recalculate defences, DCs, and monster stat blocks accordingly, which should be much easier to do, since we’ve removed so much of what used to complicate those things. The way AC is calculated doesn’t need to change, but by my reckoning the bonuses for specific armours should be scaled back by 1 for light armours and 2 for heavy armours. 

This is less crucial, but eliminate HP-per-level. Everybody (monsters and players alike) just sits at their starting HP for level 1. Scale back the damage to match (just calibrate everything around the level 1 target damage range). It’ll simplify a lot of calculations, keep monsters more relevant throughout the level progression, and reduce the damage-sponginess of high tier monsters. 

Reset the action economy: each creature gets 3 actions per round called Standard, Move, and Opportunity. Anything that used to be an opportunity action, minor action, immediate action, or free action is now one of these new Opportunity actions – and most importantly, you only get one per round. Not one per turn. So, if you take a minor action on your turn, you lose your reaction on other creature’s turns. The only kind of former “extra” stuff that we’ll keep is anything that was classified as “no action”. 

Introduce the 5E Advantage/Disadvantage mechanic, verbatim, and use it to replace the now-missing vital elements of the game, like Combat Advantage, the Marking mechanic, and some of the various circumstantial benefits of powers, feats, and magic items. If some element from 4E can’t conform to that new system, then just remove it from the game, for simplicity’s sake.