When I discussed the Titans Return line while featuring (perhaps ironically) Legends Blurr, I mentioned that the Headmaster-like gimmick was applied to nearly all of the toys in the Titans Return line. What I didn't spell out was that a very intentional part of that gimmick was that all of the small "Titan Master" heads/robots were sized so as to be interchangeable with all other "Titan Master" figures. That is to say, I could take the head off of Blurr and switch it with the head from Six Shot, giving Blurr Six Shot's head and vice versa, despite the fact that the two main robots are significantly different in size. This commitment to keeping all of the "Titan Master" figures the same size, even for the large robots, was achieved via a series of "cheats," which a review of Titans Return Galvatron will make clear.
First, let's deal with Galvatron's alternate modes. The main alternate mode is the cannon mode, which is essentially faithful to the G1 animation model (certainly more so than the actual G1 toy ever was!). If you're thinking to display Galvatron in a non-robot mode (and you may well want to if you're just getting the toy as Hasbro sold it without modifications), this is the one you'll almost certainly choose.
The other alternate mode for Galvatron is a departure from the G1 toy. I'm guessing that Hasbro was reluctant to give kids a hand-weapon mode (even with a bright orange barrel!) in this day and age (although cannons are okay?), since this mode is a rather terrible-looking jet thing (seriously, don't look at it from the back!). This mode does have an opening canopy, in which you may fit the Titan Master figure.
Speaking of the Titan Master figure, the one that comes with Galvatron is called Nucleon, a word more commonly associated with the substance that created Action Masters back at the end of Generation One. I'm really not sure why Hasbro chose that name. I suppose that they thought that calling it "Megatron" would be confusing, but that didn't stop them from making sure that Nucleon's robot mode was a dead ringer for Megatron (Galvatron's earlier identity in most continuities).
Which brings us to Galvatron's robot mode. As I said before, all Titan Master heads are the same size. They're basically scaled to be the right size for the Deluxe size class. While "Leader"-sized toys such as Six Shot compensate by making the Titan Master essentially just the face, to be enveloped by a full helmet, the "Voyager"-sized toys, of which Galvatron is representative, apparently didn't rate such extravagance (being larger than Deluxes, but smaller than Leaders). Instead, Galvatron has to make do with just a face plate that flips into place in front of the Titan Master. It's not too terrible when viewed from the front....
But when viewed from the side, the result is absolutely awful. Completely unacceptable, IMHO. For those of us willing to shell out some extra money, there are thankfully some options (although, bluntly, we really shouldn't have had to)....
Eagle-eyed readers will perhaps already have noticed that the deco on my Galvatron is somewhat different than the toy as it comes from Hasbro. This is because the option I chose came from Toyhax (formerly known as Reprolabels), which provided a nice, smooth-looking helmet (a number of other options are available at 3D-printing sites, but those all look too rough and bumpy for my tastes). When ordering this helmet, I also received a set of stickers. Although I'm not a fan of stickers (and the ones provided by Hasbro with Titans Return figures... when they had them... were inexcusably bad), I did use some of them (not all) to enhance my Galvatron figure to its current state of glory. He finally looks like he ought to.