negate an activation of effect

ok, here is a situation

my opponent have Dandylion facedown. I have Royal Oppression face up and Doomcaliber Knight. I use doomcaliber atk, and danddylion send to grave. So danddylion effect kick in, which have the effect of special summon. So can i just use oppression to negate the effect so doomcaliber does not need to negate since the effect already negated

In this case, you are sending Dandylion to the Graveyard during the Damage Step. You cannot activate Royal Oppression during the Damage Step to negate Dandylion's effect (since it is Spell Speed 2 and these cannot be activated in the Damage Step). Doomcalibur will activate and be the only thing negating Dandylion.

In the case that this was not happening during the Damage Step, the order of activation will apply. Doomcalibur is a Mandatory Trigger effect. It will activate first (before the optional effect of Royal Oppression). He will tribute himself as a cost, and then you have thoe choice to chain Royal Oppression's Optional Effect (which would be silly to do)

--The Detonator--

some more question,

i think after dandylion destroy and during send it to grave, it is not counted as damage step anymore

If Royal Oppression is face up ? I means it is not face down, this means i am not activate trap card during damage step

if all is true, this means if royal oppression is face up, other monster destroy by battle and send to graveyard and activate effect of special summon like Troop Dragon cannot be chain by Royal oppression even face up ?

Yuri Bakura wrote:some more question,

i think after dandylion destroy and during send it to grave, it is not counted as damage step anymore

If Royal Oppression is face up ? I means it is not face down, this means i am not activate trap card during damage step

if all is true, this means if royal oppression is face up, other monster destroy by battle and send to graveyard and activate effect of special summon like Troop Dragon cannot be chain by Royal oppression even face up ?

Question 1:
Dandylion is destroyed during battle like you said. Its effect activates as soon as it is sent to the Graveyard (this is still the Damage Step)

Question 2:
If Royal Oppression is face-up then only the card has been activated. You must still "activate" the effect. This is different to activating the card.

Question 3:
Yes Troop Dragon cannot be negated by Royal Oppression, neither can Mystic Tomato or any cards that Special Summon a monster when destroyed by battle. This is the Damage Step still.

--The Detonator--