Replacing 4E Rules with 5E Advantage/Disadvatnage - what breaks?

[Hawk7915]

I'm back on my 4E nostalgia kick that I get 1/year, and have been musing on if I could possibly convince some amount of my playgroup to play a one-shot of it. One thing I'm toying with is that since they're all 5E-exclusive players, what if...4E used 5E's advantage/disadvantage system?

What would that mean?

"Having Combat Advantage" would now just mean "rolling with Advantage". This could be gained by Flanking, by attacking Blinded enemies, r by any other effect that granted Combat Advantage (Invisibility, various class features and feats).

You'd roll at Disadvantage in any situation where an enemy had Concealment or Total Concealment over you.

Prone would now be: "Ranged attacks against you are at disadvantage. Melee attacks against you are at advantage. Your melee attacks are made at Disadvantage".

We'd mostly keep but reverse cover rules to be like 5E as well - 1/2 cover is +2 to Armor and Reflex (or all defenses?). 3/4 cover is +5 to the same.

This seems small but as far as I can tell, has huge repercussions:

• This is a huge attack boost in melee compared to prior combat advantage. Melee attackers are way more accurate now, but melee enemies are way deadlier.
• Crit fishing is easier than ever. Every feature, weapon, feat, and item that triggers on Critical Hits is at least 50% more powerful now.
• AoEs are scary since everything in 5E is an attack, possibly scary enough to rule that "you can't roll Area/Burst/Blast powers at advantage"?
• The Avenger is worse without exclusive access to multi-rolling Accuracy. Is it worse enough that Oath of Enmity would need a buff?
• Expertise is less essential and accuracy is less everything...but, finding ways to get "Combat Advantage" are now mandatory and every class needs to be seeking a way to get Combat Advantage on all attacks.
• Defenses are now the stat that are trailing behind, possibly to the point that Improved Defenses needs to go to +2/+4/+5, class defenses need to go to +2, and all AC needs to go up by +1 or +2 AC provided so that a PC isn't getting insta-gibbed by the first invisible or pack tactics monster they encounter?

What do ya'll think?

[sandmote]

Specifically for a one shot with new players I'd ban the Avenger (which I think needs a buff as is) and grant a +2 to all defenses. I'd actually just say the defenses are 12 + the bonuses, actually, to keep the explanation simple.

Then just switch the terminology for how cover works (great idea by the way, definitely stealing that) and call it a day. You don't need to make it harder than it is.

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If you want to put in the work to rebalance 4e to work with 5e advantage I'm willing to help try, but making the players learn 4e and simultaneously learn a bunch of rules changes to rebalance it for 5e style advantage sounds like an unnecessary hassle.

[Hawk7915]

Thanks Sandmote! I think if I can manage it (and it's a long way off - my IRL playgroup currently has 3 different 5E campaigns running, one of which I'm DMing) maybe we'll just enjoy the majesty of D&D 4E as is. It was a fun thought exercise though.

[MwaO]

The way I would do it is the following:
If you have a conditional +1 to +3 to hit from any source, you get lesser combat advantage. Roll twice, throw away even rolls on the 2nd die.
Conditional +4 or greater? You get combat advantage, roll twice.

Lesser Disadvantage is throw out the odd rolls. Disadvantage is roll twice, take the lower.

This duplicates the functionality of Advantage/Disadvantage without causing some chaos. If you have Combat Advantage and double roll, add +4 to hit(Avengers). If you have Combat Disadvantage and are taking willing dumb penalties, you roll twice and take the dumb penalties above and beyond -4 to hit. As an example, "Oh, I'm blind, so I might as well use power attack!"