There are 3 main things that make Xyz Monsters unique. There's their summon method, like with any mechanic. There's also the fact they have Ranks instead of Levels. Finally, there's the way they keep Xyz Material attached. For each of these aspects, I'm going to be discussing their benefits and design intent, as well as their issues. Also, I'll be comparing them to two other Summoning methods. Synchro Summoning was their first try at a new monster type. It was fun, but not perfect, and a lot of the design of Xyz Monsters seems targeted at its flaws. Meanwhile, Link Summoning is quite similar to Xyz, but seems to have some issues that the design of Xyz Monsters specifically avoided.
The Design of Xyz Summoning
To Xyz Summon, you "overlay" 2 or more monsters of the same level. Some Xyz Monsters perform "Xyz Evolution", which is similar to Contact Fusion. That's because it replaces the mechanic with a special method written on the card. This is usually using one other specific card as material, often another Xyz Monster.
The Reasons
The basics of Xyz Summoning are very simple and easy to understand. Anyone can find 2 monsters of the same level. It also has the potential for interesting level manipulation support, like Tannhauser Gate. It also gives levels from 9-12 a purpose. Before, they were too high for most Synchro plays and the same as 7-8 for Tribute Summons. The mechanic is fairly generic, enough to give many decks access to some useful tools. Xyz Evolution also introduces interesting possibilities for designing Xyz Monsters. For example, Beatrice, Lady of the Eternal encourages hand management,and Sheorcust Dingirsu introduces Xyz to a deck that couldn't support it before. Xyz Evolution also circumvents some issues with combo potential I'll discuss in the Ranks section.The Issues
It's a fair point that being generic isn't always a good thing. The "Rank 4 Toolbox" overtook the unique identity of many decks. While careful monster design can avoid it, Xyz Evolution is often completely free, which removes choice from the game. Very often an Xyz Evolution is either always better or occasionally always worse than the base form. Since there's often no cost of any kind, you can just decide which is best and ignore the rest. When's the last time you saw a Utopia that wasn't underneath The Lightning? These free summons played a major part in Zoodiac's domination - Zoodiac will come up a lot as a case where the design of Xyz Monsters went wrong.
Compared to Synchro
To Synchro Summon, you add up the levels of a Tuner Monster and some non-Tuner monsters. They're sent to the graveyard to summon a Synchro Monster with a level equal to the total. Tuner monsters were invented just for this, so old deck themes didn't have any. Compared to Xyz, this makes it harder to use Synchro in a deck not dedicated to it. Of course, whether being less generic is good or bad is hard to say.
Compared to Link
To Link Summon, you just send 2 or more monsters to the graveyard. Well then, if Xyz is maybe too generic, Links definitely are. While Firewall Dragon was legal, almost any deck that could summon a lot became a bad attempt at Extra Linking, down to random things like Ninja. Even now, Knightmares have largely overtaken the Rank 4 Toolbox.
The Design of Ranks
Most monsters have a Level, represented by a number of orange stars in the top right. Xyz instead have black "Rank" stars in the top left. That might sound silly, but for the purposes of mechanics and card effects, they're completely different. The main point is that Xyz Monsters don't have a level at all.The Reasons
The reason Xyz Monsters don't have Levels is because you need Levels to Xyz Summon. When designing Xyz Monsters, Konami wanted to make sure people couldn't use them as materials for other Xyz easily. After what happened when Zoodiac ignored this design principle, that seems like it was the right decision.
The Issues
Konami designs every card with certain assumptions in mind. Before Xyz Monsters, designers assumed that every single Monster had a Level. Ranks broke that assumption and required special rulings that Level-based things don't affect Xyz Monsters. It's a common point of confusion for new players and one-shot anime villains that having no Level is different to Level 0. It also means they don't play nice with Synchro Summoning.
While the lack of combo potential is deliberate, it can also be kind of a shame. The plays in many Xyz decks can be kind of boring, you just make one monster and you're stuck with it. When ZEXAL II wanted to expand the design of Xyz Monsters by adding the Rank-Up mechanic, it had to introduce bricky "Rank-Up-Magic" Spell Cards. For a few reasons, these are almost impossible to search. Because of this, any Xyz Monster that have to be summoned with Rank-Up-Magic are almost unplayable.
Compared to Synchro
Synchro Monsters have Levels the same as any other card before them. It's perfectly possible to use a Synchro Monster as Synchro Material. This isn't anything broken, though. If you don't need to do it, it's more of a waste than anything. If you do need to, on the other hand, it's part of "Accel Synchro", the way Yu-Gi-Oh! 5Ds expanded the mechanic in its second half. This feels like a natural extension of Synchro Summoning, compared to the tacked-on nature of Rank-Up-Magic. The idea of climbing the so called "Synchro Ladder" was also a key part of many combo-oriented Synchro decks before Master Rule 4.
Compared to Link
Link Monsters also don't have a Level, and they don't have a Rank. They also don't have DEF points, or the ability to go into Defense Position, including face-down. And now you can control more than 5 monsters, and the zones aren't all in the same row. If giving Xyz Monsters Ranks broke some old assumptions in card design, Link Summoning messed up almost everything. Unlike Xyz, Link Monsters allow using others as Material. In fact, it's a central part of the mechanic. This "Link Laddering" causes a bunch of problems. For example, a Link Monster needing Effect Monsters as materials to prevent Token abuse is meaningless, because there are other Link Monsters that can use Tokens and are Effect Monsters.
The Design of Xyz Material
Xyz Summoning doesn't send the materials to the graveyard. Instead, the materials are "attached" in a pile underneath the Xyz Monster. From there, they can be detached by card effects, sending them to the graveyard. Detaching a material is very often the cost for an Xyz Monster's primary effect.The Reasons
Materials are key to the design of Xyz Monsters. As well as being the most obvious difference in terms of play experience, they have multiple different design purposes. For one, the fact they're not sent to the graveyard during the summon is another limiter on combo abuse. Sangan doesn't get its search effect, and there's nothing in the graveyard to revive for loops. The other main thing Materials achieve is acting as a resource cost for effects. If a card has to detach Material to use its effect, it can only do so a few times. Notably, if you revive an Xyz it has no material, and can't use such an effect at all!
Materials have some minor incidental benefits too. For one, Tokens can't be used. This prevents situations like Scapegoat being a free Rank 1. Another upside is the interesting new design space for effects to work with. For all of Zoodiac's problems, materials granting effects that can be swapped out by attaching different materials was a great, unique idea that can only exist thanks to the design of Xyz Monsters. The brand-new Time Thieves are another example. Redoer attaches Spells and Traps, then detaches them for more powerful effects than it gets by detaching a monster.
The Issues
There's a lot in common here with the downsides of Ranks. Materials cause rulings confusions, to the point that even TCG staff originally thought Sangan would activate when detached. The intentional hampering of combo potential can be a bit much and makes decks more linear and boring. Another issue is how the resource cost aspect doesn't always work out. Normally you'll only use an effect once anyway. After that, you're opponent will probably destroy it, or you've already won. This makes detaching a material barely a cost at all. Another issue is that cards have to be designed around the Xyz Material restrictions. Some Xyz Monsters have their most important effects ignore Xyz Material, making the whole thing seem arbitrary.
Compared to Synchro
Synchro Materials are sent to the graveyard, and they can be Tokens. This led to strategies like Plant Synchro, which would abuse "floaters" like Dandylion for excessive amounts of free Synchro Material. Strategies like this were so powerful that cards like Dandylion were banned for ages. These are the main things the design of Xyz Monsters intended Materials to prevent.
Compared to Link
Almost immediately after Dandylion did get unbanned, Links came out and they had to put it straight back to Forbidden. Link Materials also can be Tokens and go to the graveyard, and they prove exactly why Xyz Materials don't. With material being easier to use than Synchro, countless cards like Scapegoat, Gofu the Vague Shadow, and Galaxy Tomahawk are on the banlist for their ability to generate free material. And like how some Xyz don't use materials, cards like Crystron Needlefiber ignore what's unique about Links by doing nothing with their arrows, which other cards use to restrict effects.
A Note on Power
An experienced reader might find some of what I have to say strange. Here am I saying the design of Xyz Monsters is inherently balanced, but they're all broken! There are more banned Xyz Monsters than every other Extra Deck type combined! How can this be?
Well, I have an opinion on why this might be. The reason is exactly because Xyz are so "balanced". Designers tried to compensate for the lack of combos and inherent effect cost by making individual cards stronger - too strong. Other cases like Zoodiac, as I've mentioned before, are broken because they ignore some of Xyz's built-in power limits. Ironically, Galaxy Tomahawk is banned because a different mechanic was designed in ignorance of the design of Xyz Monsters.Conclusion
I won't tell you how to feel about Xyz as a mechanic. While I can't claim I've been completely impartial, I didn't write this to convince you one way or the other. I just wanted to explain the theory behind some aspects of the design of Xyz Monsters that might seem weird at first glance. Whether you think that theory worked in practice, or if it's worth the downsides, is your decision to make.
As for my personal opinion, I'm a bit mixed. I really enjoy when Xyz decks can do something unique. Phantom Knights can actually search their Rank-Up-Magic, and it's one with few enough restrictions to allow interesting tech choices. That makes it one of my favorite decks. Time Thieves are shaping up to be a fun gimmick too. On the other hand, making good Xyz cards can take a level of card design Konami isn't always up to. I know I've mentioned Zoodiac a lot, but they're a prime of example of how wrong things can go. On a less extreme note, "normal" Xyz decks like Tellarknight that often just sit on their best monster of the right Rank bore me to sleep.
Still, it's clear a level of thought went into the design of Xyz Monsters. Compared to Link Monsters, the difference is night and day. Whether or not you believe the end result worked out, I can appreciate the idea behind it. Hopefully in the future, Konami learns more from its own history. If future mechanics are designed as carefully as Xyz Monsters, or even moreso, I think there's a lot of potential for good things.
