Their resolution works linearly as a queue. After the use of 1 Spell Cut-In, you because there is still a spell to cut-in on, you may play your 2nd Spell Cut-In. You repeat this as many times as you want.
by the way, on about Lock You, it's lrig type, not lrig name, right?
And if say, I uses Mayu and I have three Rikabutos on field. I activated dark matter and trash one opponent's signi and one Rikabu. And I got 3 ener because of Rikabus. Can I use the ener for another arts? And does ARTS effect resolves at the same time or does it have to wait; eg can 2 dark matter's happening at the same time?
ARTS are not used in a "stack" if that is a TCG term you are used to; you don't queue up a bunch of ARTS you wish to use during the Attack Phase and tell your opponent, "I want to use these ARTS." Rather, ARTS during the Attack Phase work immediately when you declare their use. Then, because it is still during your Attack Phase - ARTS Step, you may use more Attack Phase ARTS.
Thus, when you play Dark Matter, it resolves and you gain enough Ener for another ARTS, you may play another ARTS because it is still within your Attack Phase - ARTS Step. You may then play a second Dark Matter. This second Dark Matter's effect then resolves, and you may play another ARTS if you wish. You repeat as you desire.
Ummm question about Violence Splash's rulings, if I use Urith, Enma of Eternal Hell skill's to decrease opponent's <Angel> SIGNI to 0 while they have Arc Gain on the field and somehow activated this card before hand, will it be banish or send to trash?
I assume it will be send to trash since that SIGNI is send to trash because Arc Gain's [Constant] skill did not effect it anymore, but just to be sure :/
However, to address your question, Violence Splash changes the fundamental game rules in which banishes are handled. Thus, rather than being sent to the Ener Zone, SIGNI are sent to the trash. Because they are sent to the trash by a game mechanic and not an effect, Arcgain (and Contempora) are not immune.
I just realized I posted from my phone and was not logged in.
Further expanding on that idea, in the same case is if you somehow banish Arcgain while you have Energe's effect active. Regardless of how you banish Arcgain and/or her <Angels>, they are being basically REDIRECTED to the trash instead of the Ener Zone after being banished.