Unless stated otherwise, a card's effect only works for the card's controller, and the controller is used as a point of reference to determine who 'the opponent' is for that card's effect.
Dark Eradicator Warlock will trigger when any Normal Spell card is activated, it does not matter who did it. He will then deal 1000 damage to 'the opponent'. Regardless of whose card caused him to trigger, it is the opponent of his controller, that takes the damage.
If Eradicator was chained to Grapha's eff targeting Ophion, then Eradicator will resolve first, tributing Ophion and destroying 1500 or less ATK monsters. Grapha's effect will then resolve. Since the intended target, Ophion, is not on the field anymore, Grapha's effect resolves with nothing happening.If Eradicator was chained to Gate's effect, then Eradictor will do its effect and since Grapha's effect will only activate after the card effect discarding it resolves, Grapha' effect will not activate. So after Eradictor and Gate resolve, Grapha will select a target, which can't be Ophion as it's no longer on the field and destroy it.
vomiting ogerett
yes
Once every turn
No, it is an Ignition Effect and can only be used in your turn.
geminis must be summoned a second time to get the effect while effect monsters only need one summon
No. It is an Ignition Effect, meaning you may only activate Snipe Hunter's effect during your turn.
Magic planter
Yes.
Standby phase is in a yugioh duel after draw phase,you could use card effect at standby phase.
Arcane Apprentice's effect doesn't mention Spell Counters in any way. Are you asking about the right card?
Read The Effect Of The Card... It'll usually say what the question mark is for... For instance, The Calculator... If it doesn't have an effect.. It's probably fake...