If you want to activate LED before Infernal Tutor resolves, you have to do it in response to casting Infernal Tutor, or you have to hope that your opponent casts a spell or ability of his own, passing priority back to you.
If the active player has not declared immediately after casting infernal tutor that They are intending to respond to it, are they able to activate their Lion's Eye Diamonds in the following situations?
I assume that means the following course of actions:
- You play an LED, you both pass, LED resolves, both pass
- You play an LED, you both pass, LED resolves, both pass
- You play Infernal Tutor, you pass.
That means the opponent has priority now, and the stack consists of Infernal Tutor.
116.3. Which player has priority is determined by the following rules:
116.3a The active player receives priority at the beginning of most steps and phases, after any turn-based actions (such as drawing a card during the draw step; see rule 703) have been dealt with and abilities that trigger at the beginning of that phase or step have been put on the stack. No player receives priority during the untap step. Players usually don’t get priority during the cleanup step (see rule 514.3).
116.3b The active player receives priority after a spell or ability (other than a mana ability) resolves.
116.3c If a player has priority when he or she casts a spell, activates an ability, or takes a special action, that player receives priority afterward.
116.3d If a player has priority and chooses not to take any actions, that player passes. If any mana is in that player’s mana pool, he or she announces what mana is there. Then the next player in turn order receives priority.
a) No. The opponent passes priority, and since all players have passed in succession, the stack starts resolving. Since Infernal Tutor is top of the stack in this scenario, you will not get a chance to activate a Lion's Eye Diamond, because you can only activate it when you have priority.
405.5. When all players pass in succession, the top (last-added) spell or ability on the stack resolves. If the stack is empty when all players pass, the current step or phase ends and the next begins.
b) No. You cannot respond to a response that way - as long as the opponent has priority, he will get to play his spells and abilities (see 116.3c). You can only activate mana abilities during that time. Lion's Eye Diamond is a mana ability, but it has the additional timing restriction that it can only be activated as an instant, so unlike e.g. a land you may NOT activate LED if you don't have priority. Of course, if the opponent has played at least one spell or ability, then you will get back priority at least once, and you can activate one or both LEDs. But the opponent can play as much stuff as he likes before that, potentially adding to the Storm count.
c) No. It is indeed the same as a). Also I'm not sure why you found it important to mention that, but players don't have to update the Storm count. It is not an action formally recognized by the game rules - "the game" (which means the players in the end, of course) tracks that for them. The only time when Storm count matters is during the resolution of a spell/ability with the Storm ability.