With the new update coming, I realise that it's going to be a little more difficult to get season rewards as a newer player. As of today, I bought $50 worth of cards to get my collection power up. This is the first time that I have gotten past the first bronze league, and I just wanted to share a card that really helped me.
This summoner gives every friendly monster the flying capability and you can use any splinter you want with it since its a dragon. I paird this with a healing tank and it helped a lot getting to the next league. If you want to see any of the other cards I got, I've attached screenshots below. They're lower cost cards just to help diversify and increase collection power.