Xtra HEROs
The Design of the cards is unknown. They seem more or less random only somewhat following the style of the original Elemental HEROs. They do have a robotic fashion to them, which may hint that they are meant to be a mixture of all the HERO sub-archetypes art styles. The name of the sub-archetype is meant to refer to the new link summoning mechanic that was introduced in Master rule 4 when Link monster were announced. With that being said they are obviously Link Monsters.
The Xtra HEROs do not have a set playstyle. Each of the cards so far is meant to assist one of the other HERO sub-archetypes. Wonder Driver sets a fusion spell from the grave which aids Masked HEROs and Elemental HEROs. Dread Decimator gives all HEROs it points to bonus attack which helps Vision HEROs attack altering monsters. Lastly Cross Crusader summons a Destiny HERO from the graveyard, which obviously aids Destiny HEROs. There is one more unreleased monster who is meant to Aid Evil HEROs.
I am hopeful that there will be more Xtra HEROs coming in the future as they are extremely useful to the overall HERO strategy.