D&D 5E Improved Invisibility vs Haste

[Huntsman57]

Defensively, I think it's clear that disadvantage on enemy attacks is at least as good, if not in most cases better than the +2 to AC Haste offers us.

On the other hand, offensively, in what situations do we prefer advantage on our existing attacks versus an extra attack? I would imagine this comes down to attack bonus vs AC and the # of attacks.

Of course, Haste is better at allowing a Gish to maintain agro, whilst II is better at allowing us to slip away if matters have gotten out of hand...although is there an official rule in regards to attacks of opportunity against an invisible target? I've been ruling that in order to get an attack of opportunity a perception check is required for the attacker to notice his opponent has left the square.

 

[Warmaster Horus]

I like Improved Invisibility better. The enemy needs to locate you before they even have that (disadvantaged) attack and invisibility allows you to (more or less) move in and out of combat without fear of AoOs (since AoOs require the target to be seen). Also, since you can' be seen your attacks are made at advantage.

 

[Huntsman57]

I guess I probably should have specified that the intended wearer of this spell is a melee gish, so again, aside from the possible ability to slip away better, the enemy will generally know which square I'm in. Of course, depending on how we're ruling attacks of opportunity, I may be able to kite around in melee as well.

 

[Nagol]

Defensively, I think it's clear that disadvantage on enemy attacks is at least as good, if not in most cases better than the +2 to AC Haste offers us.

On the other hand, offensively, in what situations do we prefer advantage on our existing attacks versus an extra attack? I would imagine this comes down to attack bonus vs AC and the # of attacks.

Of course, Haste is better at allowing a Gish to maintain agro, whilst II is better at allowing us to slip away if matters have gotten out of hand...although is there an official rule in regards to attacks of opportunity against an invisible target? I've been ruling that in order to get an attack of opportunity a perception check is required for the attacker to notice his opponent has left the square.

Per the rules

You can make an opportunity attack when a hostile creature that you can see moves out of your reach.

Invisible creatures are immune to opportunity attacks.

 

[Warmaster Horus]

Unless the opponent can see invisible there will be no AoOs ("You can make an opportunity attack when a hostile creature that you can see moves out of your reach.") for moving in and out of threat range. And I'd take Advantage on attacks over an extra attack in most situations (twice the chance to crit and an overall better chance of hitting).

Both Greater Invisibilty and Haste are concentration spells, and with the lower general likelihood of being successfully attacked with Greater Invis, with corresponding concentration checks, it will generally last longer than Haste, too.

 

[Huntsman57]

Good to know. I missed that part of the verbiage.

So that brings us to the question of advantage on our attack(s) vs extra attack, and in which circumstances one is statistically better than the other.

 

[Warmaster Horus]

Good to know. I missed that part of the verbiage.

So that brings us to the question of advantage on our attack(s) vs extra attack, and in which circumstances one is statistically better than the other.

That brings up the need to assess the situation. If you're fighting a hard-to-hit foe, then advantage is the way to go. If you're fighting low AC / low HP enemies then the extra attack is better. Typically you'll want the tactical edge against a peer opponent so I'd say Advantage trumps an extra attack (especially if you already have 2 attacks) for deciding which spell to take. Also the defensive edge of Greater Invis is mostly superior to Haste, tipping the scales heavily in that direction.

 

[HarrisonF]

I did some analysis recently on this for my wizard casting on our sharpshooter ranger. It was right around AC 16 that it switched from being haste to improved invisibility as more expected damage.

With that said, there are a lot of circumstantial cases as well where one is better than the other.

With Haste, if you have a chance of losing concentration, it can be pretty bad. Skipping a turn of actions can be devastating, so if you are a self-buffing gish, you should be very careful.
With Improved Invisibility, there are a lot of creatures that can see through it via blindsight or similar. When fighting a dragon, II isn't useful at all.
If there is already a way to get advantage, then II loses out as well. For example, barbarians find haste dramatically better than II.
The number of attacks will come into play as well. Getting advantage on 4 attacks gives a lot more gain than just one bonus attack from haste. We are only level 9, so that isn't too significant yet.

My decision tree I ended up with:

Can the monsters see through II? If so, use Haste.
Do we likely already have advantage on a lot of attacks? If so, use Haste.
Is the monster AC less than 17? If so, use Haste.
Otherwise use II.

 

[SuperZero]

...I'd say Advantage trumps an extra attack (especially if you already have 2 attacks)...

If you don't have at least two attacks, the second attack is the clear winner.
Both Advantage and a free attack grant you one extra die roll--their chance to hit and crit at least once are completely equal, but with the extra attack you have the chance to hit with both.
If you roll a 1 and a 20, either way you have one crit. But if you roll a 15 and a 16, you probably got one hit with invisibility and two with haste.

If you already have two or more, adding Advantage to them does give you more dice, and thus improve accuracy and crit rate. At that point it becomes a bit more situational.

 

[Huntsman57]

My decision tree I ended up with:

Can the monsters see through II? If so, use Haste.
Do we likely already have advantage on a lot of attacks? If so, use Haste.
Is the monster AC less than 17? If so, use Haste.
Otherwise use II.

AC17 seems a bit arbitrary. What's your attack bonus relative to this AC?

I was rather hoping to distill hard answers out statistically though I realize this has more variables than asking something like "what is the stat benefit of advantage based on relative AC and attack bonus." In this case # of attacks also have to be factored in with futzes all the hell with the possible outcomes.