Arguably the most infamous of Yu-Gi-Oh! mechanics, pendulum monsters came to be in the Arc V anime, releasing in the TCG in 2014. Pendulum monsters are unique cards in that they can be both monsters or continous spell cards.
The pendulum mechanic has had many changes over the years, from being forced into extra monster and link zones, to having the scales put in the original five spell and trap card zones. Being able to summon a bunch of monsters in one turn was bound to be a broken mechanic. While its power is often overblown, pendulum monsters are still a force to be reckoned with.
Supreme King Gate Zero is unlikely to have its Pendulum effect go off, but its status as a zero scale is what will often put in on your scale. This allows you to pendulum summon just about any monster in the game, only limited by the number on your other scale.
Its monster effect allows you to bring out link fodder, all while setting up a scale, since it sets itself there rather than being sent to the extra deck like normal. Supreme King Gate Zero builds you a ton of advantage quickly and will find a place in any pendulum deck.
Mythical Beats Master Cerberus is a part of the small series of mythical beast pendulum monsters. It can easily be used to search out any of the other mythical beast cards from your deck while placing itself in the extra deck face-up to bring back with a pendulum Summon.
During your turn, if a lot of spell counters are on it, you can banish any monster the opponent controls while gaining attack. Since pendulum monsters count as spell cards, it's incredibly easy to build up spell counters to pull this fantastic effect off.
It stands to show how powerful Endymion is when one of the weaker cards in the Archetype is still one of the best pendulum monsters in Yu-Gi-Oh! It can easily special summon itself off the scale while bringing out another monster from your hand that a spell counter can be placed on.
While on the field, Reflection Of Endymion bounce cards the opponent controls, along with a card that a spell counter can be put on. If there were spell counters on that card, they stay on the field and move to Reflection Of Endymion. This effect is so good since it allows you to recycle cards you want back on the scales.
Double Iris Magician is a fantastic card and spent a good amount of time on the banlist, only very recently going back to unlimited. The reason Double Iris Magician is so good is both for its effect and its eight scale.
It can search out any pendulumgraph card in the game when destroyed, and there's plenty of solid options, though tragically the best option is still banned. An eight scale is one of the best scales you can have, as it's so high that you will be able to pendulum summon almost any monster in your deck.
Magical Abductor is a fantastic card as both its monster and pendulum effects can be abused since they are both not a hard once per turn. While in the scale, Magical Abductor can search out any pendulum monster from your deck, so long as you have three spell counters to spare.
On the field, it can add any level one spellcaster monster, and there are plenty of powerful ones. Magical Abductor can help fix hands, all while searching out your key cards multiple times a turn to make it one of the most versatile pendulum monsters in Yu-Gi-Oh!
Mythical Beast Jackal King is a card that practically every pendulum deck will play. It can destroy itself while on the scale to search out a different mythical beast, which is done often to put it into the extra deck to bring out with a pendulum summon.
The power of Mythical Beast Jackal King comes from its monster effect. While on the field, it can remove two spell counters from anywhere to negate the effect of a spell card. Spell cards are the most prominent card type in Yu-Gi-Oh!, so having a negate that isn't a hard once per turn for them is bound to be great, and is why it is one of the best pendulum monsters in Yu-Gi-Oh!
Performapal Skullcrobat Joker is such a good card its been on the banlist since the PePe days and is still currently semi-limited. The main reason is that it is one of the best searchers for pendulum monsters in the game, and their primary normal summon. It can search out any Performapal, Odd-Eyes, or Pendulum Magician Monster.
This essentially means that you can search out for any number scale that fits your hand the best. Even if not used to search, it has an eight scale, which allows you to pendulum summon just about anything.
Performapal Pendulum Sorcerer is one of the best pendulum monsters in Yu-Gi-Oh!, and one of the best performapal cards. It has a two scale, which is one of the best low scales a monster can have. Its pendulum effect will likely never come up, as its monster effect is so much better.
When special summoned, you can opt to destroy two cards you control to search out two performapal cards with different names. This is so good since it can pop other pendulum monsters while getting two cards to set up any range of scales to bring them back with a pendulum summon.
2. Servant Of Endymion
Whenever a card lets you special summon a monster from the deck, it's bound to be broken. Servant Of Endymion is no exception, and is currently limited on the banlist. It has a low scale of two, with a fantastic pendulum effect allows both it and any monster with 1000 Attack or more that can have a spell counter put on it to be special summoned.
Servant Of Endymion is hard to get rid of as well, since if its destroyed as a monster it goes back on the scale. This allows it to re-use its effect, which isn't once per turn.
As soon as it was released, Endymion, The Might Master Of Magic became the main boss monster for any pendulum deck. When it's brought out from the scales with its own effect, it can lead to mass destruction of the field, both your own or the opponent's depending on the game state.
So long as a card has a spell counter on it, Endymion, The Mighty Master Of Magic can act as a negate for spell or trap cards. It is also near impossible to get rid of, as it is unaffected by card effects. It can be destroyed by battle, but can then be pendulum summoned back the next turn.