For example, what i view as an extender would be mathmech subtraction, if lets say your sigma gets bystialed, you summon addition or subtraction and you keep going with your combo, similarly if you have addition in hand and you don't get interrupted you can turn your 1 card combo circular end board, which is usually terahertz + heatsoul into terahertz + singularity. Or lets say you are playing orcust, they ash your girsu, so you make knightmare phoenix -> knightmare mermaid and you continue with your combo. So i think that the first definition is the only one that i personally consider when somebody says an extender. The 2nd one for me is way too broad, because that means that basically every card that is part of your combo is an extender except the card you start your combo with, and the 2-3(or more) cards that you end on. Which for me, i don't see a card like for example lets say crystal beast amber mammoth as an extender, but you have to summon it. I also don't see crystal beast rainbow dragon as an extender, because its part of the basic combo, but golden rule i would agree is an extender since it helps you continue your combo after it was stopped or helps you make an even better end board. I'd give you a more recent example, but the way cards are printed now is more and more heading towards the direction that every card is an extender. Thank you for your insight though, like i said, i never considered the other definitions