I don't think we can put and/or variables in the macro.
We can use the variable [stealth], but there isn't one for [behind].

If you attempt a macro like this:
#show
/cast Shred
/cast Mangle

If you are able to Shred, the macro fires off.
If you are unable to Shred, then the macro ends.
It does not default to Mangle, when Shred fails.

If you were to have Shred and Mangle on two separate keys.
And spam both, but with the Shred slightly ahead of the Mangle.
That might fire off.
The click command does execute top-down, but have not experimented with this.

Possibly something like:
Click Macro A
Click Macro B

Macro A
/Cast Shred

Macro B
/Cast Mangle

I tend to think, this would stick like the one macro, with both Shred and Mangle as cast commands.




I've just decided to ignore Shred, as part of my DPS.
Mangle any time and from any direction, is easier than Shred but only from behind.

I'll have a macro for attacks from behind:
/cast [stealth] Ravage; Shred

But those won't be part of my default spam castsequence.

If I'm in melee range, Mangle will fire off.
5x Mangle (one per Druid) will be decent damage.

If it is an opener in PvP, it will likely be 5x Ravage, instead of 5x Mangle.
Which then allows for Feral Charge > Ravage, without waiting for the cooldown on Feral Charge.



I'd like a castsequence, with a single button to spam.
It will be easier then actively managing a rotation on several toons.

We can Mangle, Rake, Rip, Savage Roar, Ferocious Bite, Feral Faerie Fire, etc.. regardless of whether the target is facing us or facing away from us. Which means the castsequence won't get stuck on a Shred/Ravage, if we don't have the target facing away.