You have to discard to gain cards, but that means you can get rid of cards you dont need or trigger something else
But it could easily see play in any deck with big creatures (something green specializes in)
Action cards arent quite as crucial a part of your deck as characters, but you should always look at including them in your deck where you can
Even though Cloud, Ex-SOLDIER offers additional card draw for each equipped creature, it still ends up being far better to just focus on piling everything on Cloud and protecting him rather than spreading it out: you'll kill people faster with commander damage, you'll reap bigger rewards off stuff like Behemoth Sledge gaining you way more life, and it's simply easier to protect a single creature than trying to protect your entire board
Demonic Pact is the clear standout, straight-up winning you the game if you can give it to your opponent after using its first three modes
Xanathars power really comes from the ability to just play cards from your opponents library, though