Cannot be Normal Summoned or Set. Must be Special Summoned (from your hand) by sending 3 face-up Trap Cards you control to the Graveyard, and cannot be Special Summoned by other ways. This card gains 1000 ATK for each Continuous Trap Card in your Graveyard. Once per turn: You can target 1 Set Spell/Trap Card your opponent controls; destroy that target. Spell and Trap Cards cannot be activated in response to this effect's activation.
You'll get EX Jewels during the event. That item can be traded for event exclusive cards at Card Trader EX! You can only trade each card once! The recommended cards shown below.
I got so far above 1000 gems from the lottery and chests. I enjoy these chronicles events a lot although the previous one was better as it encouraged you to play as different characters while you only need to play as Jaden on this one.
Don't Skip boxes
I just got 100 gems from one of the boxes
That's a rather rare drop, I've gotten it exactly 1 time so far (as I'm expecting you have, too.) You probably make more gems speeding through the board and getting them as drops from the lottery than trying for them in boxes.