Split second + storm

[Mulletus]

1. What happens if someone casts a storm spell with a storm count of X, and I cast a spell with split second in response to the first?

2. I cast Tsunami, my opponent responds with High Tide, I respond with Celestial Crusader (flash, split second).... can someone explain what happens next? I think they have the option to add mana before the Islands leave play, but cant use it untill they all hit the graveyard... but Im not sure.

[Nightmare]

1. Your split second card resolves, then all the storm copies resolve, unless your spell was Trickbind targetting the Storm ability.

2. Your Celestial Crusader resolves, then they have the ability to continue playing as normal, with +1 Storm.

[noobagain]

Since you mentioned trickbind; does playing trickbind in response to brain freeze counter all of the copies or just one of the copies?

[Eldariel]

Since you mentioned trickbind; does playing trickbind in response to brain freeze counter all of the copies or just one of the copies?

The only legal target for Trickbind is the Storm-trigger, which only leaves the actual spell on the stack, all the Storm-copies are nullified.

[DeathwingZERO]

2. I cast Tsunami, my opponent responds with High Tide...... I think they have the option to add mana before the Islands leave play, but cant use it untill they all hit the graveyard... but Im not sure.

This last part makes me believe you are under the impression if a Split-Second card is on the stack, that all spells resolve at the same time when it's done. When Crusader resolves, the Tide and Tsunami are still on the stack. Tide will resolve, and the opponent will have ample time to do whatever he needs to do at instant speed with his mana (if playing something like Solidarity, for example) before your Tsunami even resolves. As long as he's casting nothing but Instants, your Tsunami would still be on the stack awaiting him to stop casting.