CardName: Futile Struggle
Type: Enchantment - Aura
Rules Text: Enchant creature. It cannot block, and cannot tap except to
Set/Rarity: Community Mashup Set Uncommon
Ambush Raid + Avacynian Priest
Empty your hand. Red discard? That's a thing? And a tap-down.
Red tap? A discard creature?
Target creature attacks this turn if able (but it isnt able, you're only allowed to attack players) would work? Although the siren effect is blue. Largely because alpha cared for flavour more than mechanical identity.
And huh, you know what? Red often prefers "Cannot block" as its clue for 'must attack'. So why not do a red-style cage effect? If your creature cannot do anything OTHER than attack; well, you might as well attack with it, right?
So almost the opposite of a tap-down; and uses the "Huh, in THAT colour?" bit of the first card, I guess. Pseudo-removal and just too strange for common; but doesn't need to be rare. Can be cheap though.