MEchanics idea in search of a reason to implement it: Advantage -> Extra Attack

[Segev]

I will probably try to adapt this into something later, but wanted to throw the idea out there now. Consider a feature or ability written like this:

Once per turn, when you make a weapon attack with Advantage, you may forego that Advantage to make a second attack with the same weapon.

Alternate ways of playing with this might be having the attack be a critical hit if both dice hit, or exploring possibilities of permitting "stacking advantage" by using one source of advantage to transform into an extra attack, while still retaining advantage on the attack.

Are there ways this could be a good mechanic without being overpowered? On what sorts of builds would it be most useful? Could it work with non-weapon attacks (e.g. spell attacks, such as cantrips), and still be worded neatly?

[PhoenixPhyre]

This has the True Strike problem, but in reverse. Attacking twice is (almost always) better than attacking once at advantage. Same overall chance to crit, but you get your static twice if you hit. So unless it's attached to an ability that costs a major resource for a "hit and win" effect, it'd always be worth using. And that's a problem in my book--if something is a no-brainer "use it every time you can", it's probably not balanced well enough.

[Kane0]

Isnt that what the samurai does?

[Segev]

Isnt that what the samurai does?

Why, so he does! Good catch; thanks for pointing it out!