Most fun item I’ve had so far: a “does something when an opponent uses an item” item, enchanted with Bleed.
Related bug: it seems like there’s a rate limit on how fast that can activate. It seems to me that, given that you intentionally want to allow for broken combos, if you and your opponent both have an “use when opponent uses an item” item, then as soon as an item activates, that should activate continuously until one or the other player is dead.