They have very little interaction with the opponents field, outside of GolGars destruction
Rank 6 XYZ can be done with 2 Fusion monsters and you can make an M7 to grab a Dog from the graveyard or bounce I problem card the opponent controls, etc
He then Xyz Summoned his "Number C" through the use of "Rank-Up-Magic Barian's Force", resulting in "Number C107: Neo Galaxy-Eyes Tachyon Dragon"
This card can be fusion summoned using the spell card Fusion Destiny, which sends fusion materials from the hand or deck to the graveyard
All of the Special Summon from hand abilities are hard once-per-turn effects, so you generally want to stay diversified and avoid drawing multiple copies
I used to think, "It requires a card from your hand, isn't that weak?" I've looked at various deck lists, and many used 3 or 2 Nyannyan as the Virtual World monsters that take up the Normal Summon