Everyone has a 78 hilt / barrel mainhand. Rest of gear is also 78s and mostly optimized 78s (set bonus / good enhancements).

We have a guardian/shadow for tanks and scoundrel/sage for heals. DPS is watchman sentinel, combat sentinel (for killing anomalies), and a sage and slinger for ranged (not sure on their exact specs). We get through the first phase just fine, often beating the second set of adds for each tentacle, ie the second set does not even spawn. During second phase we throw all the DPS on right tentacle then the combat sentinel leaves as soon as the first anomaly spawns. Other 3 dps continue killing right then left tentacles while the combat sent again deals with anomalies.

We are hitting enrage during the third set of tentacles in the 2nd phase and he 1 shots the tanks and that's that. We're not even close either as we usually still have one of the tentacles at or nearly 100%.

Is this bugged/normal or do we need to start throwing healers on the tentacles too? And also have the combat sent skip the last anomaly (it still spawns) and then we deal with it during irregularties phase?

I'm pretty sure this is happening because your tanks are pushing the actual boss too far, it popped up in another thread pretty recently. Unfortunately, with the small health pool in 8-man, its easy for the tanks to push too hard, forcing the boss into a hard enrage instead of his regular tantrum. The mechanic was put in place to make sure groups don't just ignore the tentacles and focus fire the boss, but it was tuned around 72-gear. Make sure tanks watch the boss percentage, and if needed, restrict their rotations to use only the abilities needed to maintain defensive buffs.

Edit: Here's the link to the previous post of other groups encountering your same problem.

Are you having the 3 dps killing the tentacles using CDs to stay on the platform when the tentacles slam? Having one of your healers helping dps should be happening too, there isn't that much healing that needs to be done during the second phase, just have the main healer call out if they need help.

So you're saying have the 3 dps stay on platform and eat a few of the slams intentionally?

I'm pretty sure this is happening because your tanks are pushing the actual boss too far, it popped up in another thread pretty recently. Unfortunately, with the small health pool in 8-man, its easy for the tanks to push too hard, forcing the boss into a hard enrage instead of his regular tantrum. The mechanic was put in place to make sure groups don't just ignore the tentacles and focus fire the boss, but it was tuned around 72-gear. Make sure tanks watch the boss percentage, and if needed, restrict their rotations to use only the abilities needed to maintain defensive buffs.

Possible. Boss enraged at ~18%.

Yes, whenever your dps have a CD that they can use to eat a slam without dying they should be doing so.

As for the problem where tanks push the boss too far, it's very easy to tell if that is happening, is he jumping back up to 30% when the enrage that you're encountering happens?

For us it helped when we put one DPS + healer on one tentacle and other 2 DPS on the tentacle. They will be slightly out of sync but DPS uptime is better as the buff tentacles get makes uptime very low on second tentacle being killed. Also this will keep the DPS on anomalies a bit more busy.

but they go down the same if not slower that way. The longer it takes to get to 30% then longer it takes to use execution moves.