Phyrexian Colossus is thematically a better fit for this cube than Traxos, Scourge of Kroog. It contribute to the Life and Tap/Untap mechanical themes by combining them in an interresting way. On the other hand, Traxos just contribute to the Tap/Untap mechanical themes while hinting to an Historic mechanical theme that is not in the cube even if its many legendary and artifacts cards could support it. But the fact that Phyrexian Colossus is almost never picked because of its really steep costs Traxos, Scourge of Kroog a sound replacement. Depth Charge Colossus could have been a good Prototype version of its Phyrexian cousin but WotC seems to have dropped the ball on this one.

Ashnod, Flesh Mechanist would be a dubious inclusion if it wouldn't have Deathtouch wich makes it a fine one drop. Her mechanical themes are quite similar to Qarsi High Priest but the side advantage of her trade is ramping for activating abilities instead of an uncertain card advantage. I think she's a better card overall that the former but not with a high margin if not for the deathtouch.

Mizzium Tank had a custom version who tap creatures with lesser power and untapped creatures with greater power: an interresting feat but not a really usefull one in this cube finally. I'm always ambivalent about adapted cards as they should be taylored for my needs but they're also welcomed with defiance by other players if they deviate too much from their original design. In any case, Brotherhood's End bring more Sweeper and Artifact removal effects.

Phyrexian Soulgorger is almost implayable on turn three and do so little in the short time it is sustainable. Originally, the plan was to get as much counter removal as possible to keep at the lowest the number of age counters on the Soulgorger. But there will never be a critical mass of these effects even if WotC suddenly printed a bunch of them, simply because there are a lot of other mechanical needs in this cube to cater for a norrow one such as this. On this topic, Mystic Remora should stay for now as it's a potent card without shenanigans. Meanwhile, Wheatherlight Compleated contribute to the same mechanical themes as Phyrexian Soulgorger and even more !

For one more mana, Aether Channeler is a more flexible Owl Familiar. It doesn't discard wich is a drawback designwise as the card no more fill the graveyard but better for almost anyone playing it... and in any case, the drawed card will probably end up in the graveyard sooner than later. With an endless supply of card slots, both could be in the same cube.

Bloated Contaminator doesn't contribute to the Sacrifice mechanical theme as Scourge of Skola Vale did but beyond that it's a better and funnier card by any other metrics. The poison win condition isn't atteinable in this cube most of the times but as the card stand by itself, it's the first stone to a potential latter inclusion of this mechanics (even if it isn't in my current plans).