Masked HEROs
Masked HEROs are compirised entirely of extra deck fusion monsters. Well thats not entirely true. In the manga they had main deck normal monsters that were also called Masked HEROs, but there is not much known about them and they were never made into real cards. The entirety of the sub-archetype have designs based on Kamen Rider, or Masked Riders fittingly enough. It can also be said that there may be some influence from Power Rangers as well since both are originally Japanese shows.
The Masked HERO archetype has a fairly similar play style to the Elemental HEROs. Focusing solely on fusion monsters can be very powerful especially when you need one less monster than Elemental HEROs. For Masked HEROs their method of fusion is called Transformation, and the change is brought about by the Change quick-play spell cards. By tributing one HERO they can transform into one Masked HERO of the same attribute. For example Elemental HERO Bubbleman can change into Masked HERO Vapor by himself. This is an overall improvement to the Elemental HERO strategy as it allows you to create more monsters while using less resources.
There has not been a lot of support for the Masked HEROs since they came out, but there have been a few new members to the archetype over time like Masked HERO Dian, the only female Masked HERO.