[Arcane Mage S2 M+] 20 Neltharus

Be careful of Evocating if your Tank intends to use Chains for the next pull. This is why I ask him at the beginning and after he responds I can safely Evocate for my Big Burn. It's not worth doing a Burn on a pull with Chains especially on Tyrannical weeks. This is of course highly dependent on the route and how many people are going to be using Chains for a certain pull.
For Chargath, something I learned from !Mystral on the Altered Time Discord is you can Alter Time before the chains cast goes off, Blink into the boss to break it, and Alter back. This works perfectly but make sure you notify the group you will break the first chains so the debuff doesn't stack. You can also Ginvis the leap/bleed but you have to use invis when he's already LEAPING/in the air and not before otherwise it bugs out; be careful of this. I'd either stand at range to allow more reaction time or just eat the mechanic to be safe.
For Forgemaster, I save my Defensives for Might of the Forge AoE cast. I use Alter for the first and whenever it's up for any subsequent casts. You can save Ginvis for Blazing Aegis (if the boss is targetting you first, you can Ginvis to completely cancel out the mechanic.) You can see this demonstrated at ~14:30.
You can Spellsteal the Barriers of the small earthern golem adds before Magmatusk. Be sure to use Blast Wave/DB to stop Magma Conflagration from the Qalashi Thaumaturge adds. INTERRUPT MOLTEN CORE.
Magmatusk: Alter Time the AoE Volatile Mutation, Ginvis/Block Lava Spray if it goes on you, and position properly to bait the charge so boss doesn't charge to Narnia. If you have Spellstolen Barriers from the adds on the packs before this will be IMMENSELY useful for this fight. Make sure you tell the group not to Dispel the Barriers.
Alter Time the AoE cast from Apex Blazewing bird add.
Warlord Sargha: I use Alter Time as a positioning tool when I need to Blink somewhere and grab and treasure so I can Alter back to be in position of RoP/in range to deal damage to boss. Make sure to Remove Curse on CD especially on Tyrannical weeks; very useful to ease pressure on your Healer. Block/Ginvis for Molten Gold debuff.
I did rage a bit on the Tank at the end and I shouldn't have. I was a bit annoyed at how chatty he was and how suboptimal the route was. We had fairly good DPSers and could've 2 chested this.