×2Supernatural ShapeshifterDiscard the top card of your deck, and if that card is a Supporter card, use the effect of that card as the effect of this attack.
CombustionSome legends claim that each of its nine tails has its own unique type of special mystical power.
If I use Ninetales' "Supernatural Shapeshifter" attack but I don't want to use the revealed Supporter card, can I choose not to use it?
No, you cannot. If you use the attack, you must use the Supporter card if it is revealed and if you are able to.
If I'm not allowed to play a Supporter card for some reason, can I still use Ninetales' "Supernatural Shapeshifter" attack to use the effect of a Supporter?
Sure. You are not playing the Supporter, just using its effect.
If I've already played a Supporter this turn and use Ninetales' "Supernatural Shapeshifter" attack, can I still use the effect of a Supporter I discard from my deck?
Yes, you can. You are not playing a second supporter, but using its effect via an attack.