abyss encounters will make you competetive instantly so if you invest in anything, invest in that one. You will gain more gems as they aren’t too difficult to come by
first get yourself a strong cheap deck and then save. buy either abyss encounters or rampage of the forest for aliens or sylvans. also exchange super rare tickets for enemy controllers
To add on this, if you do go for Sylvans pick up a Mask of Remnants so you don't deck out and an Anti-Magic Arrows to sub out for Komushroomo if you don't already have 2 or 3 of him.
That's why you run 2x Guardioak and Restart along with the Remnants. You'll almost never deck out and you get your choice of boss monster to throw back in your deck.