Jimmy:
Pulling off this card is very challenging, at 12 cost it needs to nearly win you the game. Unfortunately, I don't think Potions Class Disaster gets you that far. It's likely to set your opponent back a few actions, but when it comes to making decisions they're in the driver's seat. This card is actually most effective if you plan on playing two during the same turn - which is a monumental task. Overall, I'd recommend you focus on other spells at a lower cost instead of reaching for Potions Class Disaster.

John: Ramping up to Potions Class Disaster is an achievement all on its own, as rarely can you afford to ramp up to 12 spells without passing by multiple perfectly good opportunities to end the game. Potions Class Disaster is trying to be the endgame for a deck that wants to force opponents to sacrifice cards in play as well as cards from their hand. Five cards from their hand is hardly worth it for 12, but 5 cards off their board can be worth it at that price. Making sure that you are controlling their hand size is imperative in a deck that wants to make Potions Class Disaster as effective as possible. Even on its best day, I don't know that Potions Class Disaster is worth the cost of admission.

Jimmy: At 9 cost, this card will be challenging to capitalize on without some prior knowledge of your opponent's hand. Enemies of the Heir (EotHB), with proper knowledge of an opponent's hand is actually a great set up for Potions Class Disaster. Thinning your opponent's hand before forcing them to make choices will make their life more difficult. Also, EotHB is good in multiples - you might be able to play 2 in a row and obliterate your opponent's hand entirely. The one source of combo-potential for this card lies in its ability to replace Dobby's Help - instead of forcing an opponent to draw 10 cards before hitting them with Venomous Tentacular Juice, you could hit them with 1-2 copies of VTJ and follow up with Enemies of the Heir to defeat them with the damage. While potentially not as effective as using Dobby's Help you won't need to play Charms Lessons, potentially increasing your consistency.

John: Enemies of the Heir Beware is the same cost as the deadly Venomous Tentacular Juice, so it puts it within the realm of a playable cost that we may already be ramping to. EotHB is a late-game card, and as such is almost always going to be trying to stall your opponent while the clock ticks forward on your true win condition. Being able to take all of the action out of an opponent's hand by naming spells or creatures late can be devastating against the right deck, but it's a hard sell to not just attempt to play VTJ and win the game instead if you are building up to the requisite lessons for EotHB. One benefit of EotHB is that it is able to be effective against a range of hand sizes and is one of the few things that can disable an opponent with an overly large hand without discarding their entire hand or finishing them with VTJ. I like the concept of punishing an opponent for keeping certain things in their hand, but overall I think the cost would have to come down on EotHB for it to see a lot of play.