I've been really wanting to play Commence the Endgame but have struggled to find an amass deck that can make the cut. This is the first deck I've played that really feels like it takes advantage of the power of amassing with Commence the Endgame, but also has the ability to stay in the game until that's relevant.

Generally the strategy is: 

- Control the board early game with red damage, overseers, and Kefnet

- Clear early threats with Widespread Brutality as needed

- Commence the Endgame at the end of their turn to enable a good follow-up Widespread Brutality

- Finale of Promise for X >= 6 to re-play Commence into Brutality and swing for the rafters

Some more of my thoughts below. Please let me know what you think - suggestions or critique welcomed. 

Why did you include...

Invade the City

This card was one of the original ideas of the deck - but being a sorcery and not having a base Amass amount, it just hasn't really panned out. I'm keeping it in until I get some [Dreadhorde Invasion]s, but I'm honestly not a fan. 

Crash Through

This is in to seal the deal when you make your big swings - if Brutality didn't pan out and they have guys up to chump, Crash Through will change the blocking equation in your favor. It also throws another card in the yard for Invade very early. 

Gleaming Overseer

He's good at holding off nasty red beaters and keeping your army safe until it's time to Commence the beating. He has also been good counter-bait opening up the way for Kefnet on the following turn.

Lazotep Plating

This card is great at achieving two of our purposes - putting down a base Army during the opponent's turn so it can swing in ours, and protecting same army. For BO3 I'd consider another copy in the sideboard to bring in against removal heavy opponents. 

Chemister's Insight

Great draw, plays very nicely with Kefnet. 

Search for Azcanta // Azcanta, the Sunken Ruin

Fix, draw, and dumping cards into the 'yard for Invade the City.

Did you consider...

Dreadhorde Invasion

I ran out of wildcards ~5 minutes after the expansion came out, so I didn't have any to craft Dreadhorde Invasion. If I had any, I think Invade the City would be my first cut. It's been "okay" at best. The most I've gotten out of it so far has been a 5/5, which was semi-relevant (but I still lost that game). 

The Elderspell

Yeah, there are a lot of planeswalkers out there right now. I've tried running this main, but there are too many situations where it's a dead draw. My thought for now is to put it in the sideboard if you're playing best of 3. 

Sinister Sabotage

I had a few in originally but I tried to shift the direction of the deck toward synergy with Kefnet. Again the first card I'd cut would be Invade the City. If you drop Invade, then you should probably also go down to only 2 Azcanta, leaving you another spot for sabotage. 

Nicol Bolas, Dragon-God

I also had the new Nicky-B in my first pass of this deck, but he's not really a good fit here. We're not playing a lot of black - just overseer and brutality. Getting to BBB by turn 5 is tough and it never felt like it was the 'right time' to play him. 

Enter the God-Eternals

Honestly, ran out of wild cards before I could make any of these. I'd probably try a couple - 5 mana spot is open and 4 damage lightning helix isn't something to sniff at. 

[Other Amass cards]

Grim Initiate - Not really looking for small creatures

Callous Dismissal - Too slow

Lazotep Reaver - See Grim Initiate

Aven Eternal - It's alright, but this isn't really a creature deck

Bleeding Edge - Too slow

Honor the God-Pharaoh - Haven't tried this yet, might be okay, especially with Kefnet? I might try replacing the Invade's with this at some point

Toll of the Invasion - Feels a bit slow, but might be okay. Would need to test it in a more hand-control-geared version of the deck

Vizier of the Scorpion - Not a creature deck, not enough tokens to make this relevant

Angrath, Captain of Chaos - I had two of these in initially but they feel too awkward. Would put them in the sideboard probably to bring in against control decks. The menace was surprisingly relevant for allowing the army to bypass a creature to kill their planeswalker

Crush Dissent - Mana leak is mostly good because you don't have to leave up four mana to threaten counter

Dreadhorde Twins - Draft card at best I think

Herald of the Dreadhorde - Draft card at best I think

Relentless Advance - Draft card at best I think

Eternal Skylord - Draft card at best I think

Invading Manitcore - Draft card at best I think