The rest of the deck is pretty straightforward: a second Skarmory with any tool has room on the Bench until you need it, and can be swapped in to deal damage before being KOed , allowing Solgaleo ex to sweep back in for the final blow
Some cards naturally have synergy with each other and are always great to put together in a deck
There aren't a considerable amount of multicolored creatures running around in Standard, but Raffine, Scheming Seer, Glissa Sunslayer, and Bloodtithe Harvester come to mind
This normally includes all land cards, any other cards that have no mana symbols where their mana cost would appear, tokens (unless the effect that creates them specifies otherwise), and nontraditional Magic cards
Intrepid Adversary also just scales more easily with the ability being paid in two-mana increments as opposed to three