Built to Rule!

Hasbro's first attempt at capturing some of the "construction block" market pie, 2003's Built to Rule! line attempted to blend the play patterns of some of Hasbro's top brands with LEGO-compatible brick-based construction. For the G.I. Joe and Tonka sets, this meant buildable vehicles with "traditional" brick-compatible action figure pilots. For Transformers, this meant building the robot and vehicle modes around a generic transforming core.

One of these concepts worked far better than the other. Guess which one.

Virtually every set also included some other action gimmick, usually a spring-loaded missile launcher, but electronics and gear-systems also made their way into later sets.

The line was incredibly short-lived, lasting barely a year at normal retail. The second series of Transformers sets only had a limited, test-market release initially in and around Cincinnati, Ohio. The sets later filtered out into some Tuesday Morning, Ollie's, and TJ Maxx chain stores at drastically dropped prices. (It is uncertain if the second-series Joe sets shared a similar fate, but it's highly likely. Tonka was dropped from the lineup after the first series.)

Despite this failure, Hasbro would try their hand again at the construction-block market a few years down the road with the more traditional, and more successful, Kre-O.

Construction

Armada Trans-Skeletons (Smokescreen & Swindle)

Energon Trans-Skeletons (Optimus Prime & Inferno)

The Transformers Built to Rule! sets were centered around the premise of the "Trans-Skeleton", a generic "block" that transformed into a generic robot mode, with the parts added to each making up the individual robot and vehicle modes. Trans-Skeletons came in a variety of sizes and styles over the course of the line's short lifespan.

For the initial series, based on the then-current Armada franchise, the larger Trans-Skeletons came in three different sizes but had the same general construction: a flat plate with raised corners to mount wheels on, and swivel-out arms and legs. Unfortunately, this design was pretty heavily flawed, with the results being awkward, top-heavy hunchbacked robots (the "heads" were just face-plates applied between the shoulders) that looked like a plate with stick-limbs and random bits slapped all over it. The smaller Skeletons had knee-less legs crammed right next to each other, making stable posing that isn't "ramrod straight" difficult. The larger Skeletons' legs were spaced slightly wider and added knees which would in theory help with posability, but the limbs were the same 2x2 thickness as the smaller sets, leading to extremely top-heavy robots with more joints to fail to support the weight.

Each Armada kit also came with their partner Mini-Con, made up of a tiny Trans-Skeleton with a whopping three add-on pieces: two vehicle-mode shell parts (a few added an extra "turret" part) and a "head" plate that also served as a Powerlinx port for use with the dedicated Powerlinx 2x2 plate (that was theoretically supposed to attach to the rotating triggers of the missile launchers but almost never did according to the instructions). This Powerlinx plate can be used with normal Mini-Con toys, but it's not the most secure fit. The Mini-Con robot modes, however, were stuck with their arms sticking to the sides like scarecrows thanks to the vehicle-shell skirts they wore, plus the bottoms of their "feet" didn't have stud-holes so they couldn't stand securely on the kits. Oops.

A new design for a Trans-Skeleton sized between the Mini-Cons and "large" sets was designed for late Armada, but the kits were canceled and reworked for the second series of Transformers Built to Rule!, now based on sequel series Energon. This series also introduced a larger Trans-Skeleton based on the same general concept: a blockier, more traditionally-proportioned robot mode where the limbs made up large chunks of the vehicle-base, plus a dedicated flip-out neck-swivel for a full head piece rather than just a plate, leading to a better-looking robot mode overall.

Unfortunately, the Energon sets saw super-limited release as noted above... and those sets still had one of the big problems of the Armada sets, in that the builds relied heavily on huge specialized pieces of vehicle mode with exceptionally limited use in robot mode. While the vehicle builds would use all the parts (even if the robot faces were hidden), the robot builds almost invariably left a considerable number of parts unused. While the building-block concept meant the builds could be altered, trying to find a place on the robot to attach a 10-stud-wide hunk of car bumper, or an entire hood "shell", in a way that didn't just look like hanging massive useless kibble off the bot, could prove troublesome at best.

Toys

Armada sets

Mini sets (Canceled) Ramjet Rollout		Small sets Demolishor with Blackout Night Attack Demolishor with Blackout Jetfire with Comettor Smokescreen with Liftor		Medium sets Hot Shot with Jolt Red Alert with Longarm Starscream with Swindle Thundercracker with Zapmaster		Large sets Optimus Prime with Sparkplug		Night Attack Demolishor, the most interesting thing to come from the Transformers BTR line.
Very large sets Megatron with Leader-1 / Cyclonus with Crumplezone

Energon sets

Small sets Inferno Skyblast

Medium sets Ironhide Starscream

Large sets Optimus Prime Scorponok

Scorponok

Notes

• It seems very likely that Korean toy company Oxford, who manufactured the first few years of Kre-O bricks for Hasbro, was also responsible for Built to Rule! Several of the smaller, very distinctive "techy" pieces in Built to Rule! ended up replicated in various Kre-O sets.