If it is the only creature you control or one of two creatures you control, you must sacrifice it
Unfortunately, Pokemon TCG Live seems to be doing away with that, as a brief support article on the Pokemon website plainly states, "Players will not be able to trade cards with other players within Pokmon TCG Live." The decision to remove trading from Pokemon TCG Live is a head-scratcher for sure, and one that we can only hope The Pokemon Company reverses before launch
Often, I see people try to go for a win at the wrong time, get stopped, and then almost completely give up, not just because they get stopped, but because their deck no longer has the tools to win
Arms Of Hadar will have a spot in any deck that runs black, as it will shut down plenty of small, fast aggro decks
Just look away
And you don't have to worry if you Cascade into a creature