One word of caution: You don't usually want cantrips that do nothing for you on boards with discard attacks, as keeping the cantrip in hand always carries the risk that you will draw something worse than you discarded. I don't think it's as bad with topdecking, but it's still bad enough and Demagogue seems so weak that I can't imagine ever using it. Either the board allows for its attack to be so good that the downside on play is worth it, and then it still harms itself more than decks without it. Or there are ways like Library or Lookout to soften its downside on play, but then its attack is not worth it. You never get out with more than you sacrifice here.
I could combine it with Cipher?
Cipher Action - Attack, ?
+3 Cards
Choose one: Put a card from your hand onto your deck, or discard a card.
Whichever you do, each other player with 4 or more cards in hand does.
It seems alright, but there's something about the card I just don't like.
I could make it a Silver variant.
Demagogue Treasure - Attack,
You may put a card from your hand onto your deck.
If you do, each other player with 4 or more cards in hand does.
You may discard a card.
If you do, each other player with 4 or more cards in hand does.
I think I like that a bit better, but meh.
Maybe this just isn't a good card to make.
Here's something I came up with that has little to do with the above card. It's like a lab, but sits on your Tavern Mat until you discard.
Cooper Action - Reserve,
+2 Cards
+1 Action
Put this on your Tavern Mat.
--
At the start of your turn, you may call this to discard a card.
Then there's this:
Angry Mob Action - Attack - Duration,
Now and at the start of your next turn:
Each other player discards down to 3 cards in hand, then draws a card.
Wait. I forgot that delayed attacks cause tracking issues when a Moat is revealed.
Demagogue Action - Attack,
Choose one: +1 Card and +1 Action; or +2 Cards.
You may put a card from your hand onto your deck.
If you do, each other player with 4 or more cards in hand does.
You may discard a card.
If you do, each other player with 4 or more cards in hand does.
Or I could make it an attack Village:
Warriors' Village Action - Attack,
+1 Card
+2 Actions
You may put a card from your hand onto your deck.
If you do, each other player with 4 or more cards in hand does.
You may discard a card.
If you do, each other player with 4 or more cards in hand does.