If an opponent casts a spell and then Captain Mar-Vell enters the battlefield under your control later in the turn, you may cast spells as though they had flash that turn as long as you control Captain Mar-Vell
You should see it at checkout and the general details are here
Sun & Moon Sun and Moon is a whole new generation for Pokmon and was the first set to ever print GX Pokmon
(And it isn't really life drain as it sets your life to 20 every turn!) The real trick is cheating this early
While there are guidelines to keep in mind when deck building (no Game Changers in Exhibition or Core, no mass land denial through Upgraded, etc.), the bracket system is emphatically not just "put your deck into a calculator, get assigned a rank, and be ready to play." I deeply appreciate the tools that websites like Moxfield and Archidekt have put together to give you an overall estimate, and they've done some fantastic iteration to help emphasize intent as wellbut I want to stress that any estimate is just an estimate
Each artifact of yours that comes into play under your control gives the Cannoneer a +1/+1 counter and makes the turtle unblockable for the turn