Details of Energy Regen Issues in TBC Classic

Energy regeneration went through a few iterations from 2007-2009 that had unintended consequences on the playstyle of feral druids. The TBC Classic beta has similarly gone through several iterations on the regen system, each of which has had significant impacts on the core DPS rotation and enjoyment of the spec. This post outlines the changes that occurred originally and in beta, and their consequences for feral druids.

Original vanilla regen system:
-Mana and energy regenerate discretely on a fixed 2 second tick that never changes.
-The current regeneration rate is used at each tick to determine how much of each resource to return. So for example, if Innervate is cast just before a tick, that tick will exhibit boosted mana returns.
-For other classes, this caused some inconsistent behavior where ticks of Innervate and Evocation could be "wasted" depending on the timing of the cast relative to the tick timer.
-For feral druids, this system produced the powershifting rotation (with Wolfshead Helm and the Furor talent) which became a defining feature of the feral playstyle in vanilla and TBC.
-This system persisted throughout vanilla, 2.0, and 2.1. As such, the original regen system was present when all TBC raid content before ZA was current.

TBC powershift cycle using vanilla regen:
t=0, shift, 60 energy
t=1, tick, 80 energy
t=1.5, Shred, 38 energy
t=2.5, GCD ends, wait
t=3, tick, 58 energy
t=3, Shred, 16 energy
t=4, shift, 60 energy

This is the fun and engaging playstyle that feral druids have come to love in WoW Classic.

TBC 2.2-2.4 regen system:
-Mana and energy regenerate continuously rather than discretely server side, but the regen is only delivered client side in discrete 2 second batches. Each player maintains a personal tick timer that can be reset.
-Any change to the rate of regeneration triggers a full reset of the tick timer, as well as an instantaneous refund of mana/energy equal to the previous regen rate integrated over the time since the last tick. Subsequent ticks then return energy at the new regen rate.
-For most classes, this fixed the issues with Innervate/Evocation, as the tick reset means that the exact amount of mana regen intended by the ability is restored.
-For feral druids, this was a massive unintended nerf to the powershifting rotation. In the 2.2 system, a shift from cat form to caster form was treated as a change in regen rate from 10/second to 0, and the reverse for the shift back into cat. This means that the energy tick reset upon every powershift. In the original implementation, zero energy was instantaneously restored upon the tick reset, since the "prior rate of regeneration" was 0 in caster form.

TBC powershift cycle using 2.2 regen:
t=0, shift, 60 energy
t=1.5, Shred, 18 energy
t=2, tick, 38 energy
t=2.5, GCD ends, wait
t=4, tick, 58 energy
t=4, Shred, 16 energy
t=5, shift, 60 energy

This slows down the cycle by a whole second, causing a 25% loss in yellow damage. More importantly, it makes the rotation much much slower to play, and it feels more like playing a rogue waiting for multiple energy ticks before being able to cast.

TBC Beta Regen System:
-The current implementation on beta matches the 2.2 system except for one difference: the regeneration rate in caster form is still treated as 10/second, so spending time in caster form between shifts recovers some of the lost energy from the tick reset.
-The way this is implemented doesn't match either 2.0 or 2.2 for ferals, and is internally inconsistent. If the regen rate in cat and caster are the same (10/second), then shifting between the two shouldn't be triggering a tick reset at all. On the other hand, if the regen rate in caster is actually 0, then zero energy should be refunded on a powershift as in the 2.2 system.

TBC powershift cycle using beta system and perfect play:
t=0, Cat Form + startattack, 64 energy
t=1.5, Shred, 22 energy
t=2, tick, 42 energy
t=2.5, Shred, 0 energy
t=3.1, cancelform + stopattack
t=3.5, Cat Form + startattack, 64 energy

By spending 0.4 seconds in caster form each cycle, we can hack together an improved rotation that doesn't require us to wait for a whole extra tick due to the extra 4 energy restored each shift. This rotation is very clunky and unintuitive to play, however. It requires extremely precise timing to cancelform at the correct time to get the correct energy back without wasting autoattack uptime, and the energy return varies depending on the player's latency, which is awful design.

Desired Regen System:
-The feral community would like to request the following change in the spirit of #somechanges: keep everything about the current regen system the same, except give us the partial refund on an instantaneous powershift rather than requiring time spent in caster form. So in the above example, rather than needing to clip the GCD and cancelform awkwardly, the player would simply powershift as normal at 3.5 seconds and end up at 75 energy (60 + the 15 that is refunded from the previous tick).
-This change would preserve the spirit of 2.4 regen, with personalized ticks that reset, but would also preserve the dynamic and fast-paced nature of feral powershifting without depending on high APM and low latency to work. The rotation would be different from the vanilla rotation, which is fine since it's a different system, but would be more consistent with the spirit of the change. There's no reason why that 15 energy should just be lost in the void upon a powershift. When you cast Innervate mid-tick you get the proper refund when the tick resets, the same should be true for shifting mid-tick.