1 Pendulum Monster + 1 LIGHT Monster Must first be either Fusion Summoned, or Special Summoned by sending the above cards you control to the Graveyard (in which case you do not use "Polymerization"), and cannot be Special Summoned by other ways
1) when that effect resolves
It is great if Magnificent Map or Advent of Adventure are on hand since they can search for (or banish) the true combo starter of the Deck
Of course, it is equally difficult because it requires a lot of preparation, starting with filling the conditions for summoning GBHunter in advance with 2 cards of Blue Sky Lightning + Zushin's hand
It's still going strong on Master Duel though, using little Rokket monsters to get started, building up to terrifying link threats like Borrelend Dragon - which can wipe a board, grab you another Rokket, and is a nightmare for your opponent to remove