Take your time getting to used to playing 60-card Casual, as you have plenty of time lately to get to grips with more niche formats
You rarely recover from many of these destruction moves, as only one card, the aforementioned Song of Inspiration, allows you to bring creatures back from the graveyard
I think the "both is good" argument for Valki and Tibalt is that they'll be good together but there's no added value
I did play some games with Armored Skyhunter, but I think its firmly a card that wants to be played in builds that aim for extra combats, which help to balance out the hits and misses
The right play is going to depend on the matchup (if they're a very fast deck it could be right to block), your hand (if your next play is a Ghoulraiser and your creature is instead a Walking Corpse, it is excellent to block), and your tribe along with your deck