House of X #3 provided an infographic detailing the progression from basic Sentinels to Nimrods. Under the heading of "Sentinel [Alpha]," it says:
Non-sentient, mutant-hunting robots
based on non-replicating, adaptive technology. [Mark I - Mark VIII].
We've actually seen Sentinels up to the Mark XIII, so either this is a hiccup in Johnathan Hickman's otherwise clockwork-like plotting, or it's saying that the human-sized original ones were Mark I Sentinels (Alpha), allthe big, stories-tall ones were Mark IIs (Beta), Cassandra Nova's "wild" Sentinels and nano-Sentinels were Mark III (Gamma) and IV (Delta) respectively, and so forth. Until 100 years in the future, we make our way up to the Mark VIII, or Theta Sentinel.
The packaging for X-Men Legends Series 8 calls this figure the Tri-Sentinel, because it has three heads, but that's not right: the Tri-Sentinel is three normal Sentinels Loki smushed together and Spider-Man defeated. Buy six of the seven figures in the line (you don't need Wolverine, because you already have enough of him [and also he doesn't come with any BAF pieces]), and you can build a Theta Sentinel of your own.
Getting the heads into place is incredibly difficult, because of the way the necks are shaped: you're not applying force directly against the peg, so things just want to flex instead of popping in. We recommend giving the heads a soak in hot water to make the pegs softer, then you might still have to use the flat part of a screwdriver or the back end of a piece of silverware to push them into the torso.
The Theta Sentinel was designed by RB Silva, and definitely looks like an evolution of the stanard Sentinel chassis. When the
figure was first revealed, it seemed like it would be reusing parts from the SP//dr BAF, because they've both got those thin limbs and broad torso over a narrow waist, but the released figure is 100% new. It's smooth and rounded, with points on the elbows, hips, shoulders, and knees. The heads are on tendrils that emerge from a flat section on the front of the chest that's sculpted with tons of intricate techno details.
The Theta Sentinel is mostly a metallic lavender with silver accents and a dark grey under-body. It doesn't have any of the blue normally found on Sentinels, but it's still clearly connected. The only break from these colors is the red eyes on all three heads, and a few similarly colored stripes on the back of the arms.
Other than the head, getting the Theta Sentinel assembled is easy, It's a top-heavy design, though, so you'll need to be careful
how you pose it, There are swivel/hinge joints at the ankles, wrists, elbows, and shoulders; double-hinged knees; swivels at the thighs; and balljointed hips and chest. Additionally, each of the necks has a balljoint where it goes into the body, and a balljoint in the head, though again you'll want to be very careful moving those, lest they pop out of place and you have to reheat some water to get them back in. The sockets on the torso are deep enough that they function mainly like swivels, turning around and doing nothing else. In the comic, Theta Sentinels could extend their heads on telescoping necks, and the fingers could distend like Ghost in the Shell, but neither of those happen here. Which is probably for the best.
This series may (mostly) be based on House of X, but the Theta Sentinels only come from the century-hence future shown in Powers of X. Side note: that's read "Powers of Ten," not "Powers of Ecks," because the story jumps from the past (Year 0) to the present (Year 10) to the near future (Year 100) to the distant future (Year 1,000) - so, y'know, exponents. Xº, X¹, X², X³. 0, 10, 100, 1000. And then a later crossover is X of Swords - although it's publically "Ten of Swords," like the tarot card, it could just as easily be read "Cross of Swords." At this rate, we're not too far off from stories called "X of the Times," "X of the Beast," or "X of Death." Anyway, Theta Sentinel can hang out with Omega Sentinel and Nimrod as the anti-mutant forces of