One of the most important things in this game is achieve high numbers.This way, you can deal damage more easily or make your opponent to lose a Sentinel or a good amount of hand. Besides the usual trigger power up's, there are units that gain a certain amount of power if you do something like retiring, locking, soulcharging etc. These type of units gain power each time the such actions are performed.
The very first deck that use this strategy is the Royal Paladin deck that resolved arround these units: Young Pegasus Knight and Great Sage Barron. Both of them get power +3000 whenever you soulcharge. Nothing special you think?. True, but when combined with Demon Killer Knight, Lohengrin, Margal, Sharron, Pongal you get two power creeps able to break numbers. Even it they aren't used now, they were very popular at one point.
Such units can be found in a lot of clans but not all of them are good enough for building a deck. The best choices of such units are those who can be powered up in any phase of your turn. A good example are Thousand Ray Pegasus and Million Ray Pegasus. They both belong to the Angel Feather clan and they power up whenever a card is put in your damage zone. Since Angel Feather's specialty is swaping your cards in damage zone, it's not hard to power up this units in your own turn (as well as opponent's turn.).
However, even if they power up by doing a certain action, they can't perform that action. So, we need some cards that'll help them. So basically, what you need is a boss able to do that during the entire game. . Some clans have more than one boss , some clans only on boss eable to do that every turn. Also, since the deck is composed by grades 0, 1, 2 and 3, you can add some units that can perform this action one time a game or when it attack hits. It's your choice.
Often, the grade 3 bosses don't fall under the "meta" choices. That's not a viable arguement if the deck works great.
One great downside of such decks is their fragility. The rearguard line-up will be mostly, formed by copies of those units. Based on that, people will try to eliminate them from the field and unfortunately, dragon addicted monkeys have more than enough possibilities to do that.
PS: It's my first strategy article so if you have any objections leave them in the comments bellow.