
A trap is a special type of setup whereby player A attempts to trick player B by making threatening plays, forcing player B to deal with the threat suboptimally. In my opinion, a trap must meet 3 criteria. It must
- Present a credible threat
- Trade well with removal
- And act as both a bait and a punish
The whole point of a trap is putting your opponent into a situation with limited answers, all of which are bad. For all of the following examples, consider that I am going first, and playing a Fox Familiar on turn one. My opponent potentially has 2 to 3 mana and 5 answers. Fox Familiar is a credible threat here; if it is not answered, its fury will activate, drawing me a valuable 1 mana card and becoming a 2/4. So, not answering is not ideal for the opponent. Therefore trade with removal right? My opponent may do that, using a number of options such as Scorch, Grim Reprisal, Whisk Away, and Eye Spider. The exact card doesn’t matter. In every possible instance of removal that is used, the answer here presents an opportunity cost to my opponent. Since they used Grim Reprisal now, how will they answer any of my later threats like Mushka? With Eye Spider out of the way, how many answers do they have for my Sworn Oni? In this instance, Fox Familiar has limited the value my opponent got out of the removal option used, since the card was not used at peak efficiency. The card has traded well with removal, and opened up gaps for future plays. Finally, the most important part of a trap is that it does both of these at the same time. If it only did one, it would be more readily thought of as a finisher. Tiamat presents a very credible threat, but doesn’t trade well versus removal. Icaru trades well versus removal, but doesn’t pose much of a threat. If it sticks, there’s little payoff compared to Fox Familiar. A trap must present both a threat and a punishment if it is not answered.

Now that we’ve established the concept of a trap, it’s important to think about how it’s going to be executed. Traps work in stages. First, the unit is played onto board. This is an investment of tempo, and consequently requires that we already have tempo when we do this. Units that are traps tend to not trade well against other units; if units were used to remove your trap, then you probably shouldn’t have played it. This makes them great vs removal pile decks, but more difficult vs things like aggro and midrange. After the trap is played, the opponent has their turn where they choose a response: they can either remove it or not. If they remove it, we should now have some tempo, value, or other advantage at the end of the exchange if you did things correctly. For example, a Griff Scout may lose to Whisk Away in tempo and value, but now we are safe to drop Rubble Devil since the more optimal removal option was used prematurely. Finally, the opponent may respond with either countering units (Guard vs Glory) or by developing their own threats. Now we punish. In the majority of situations where the opponents answer by playing units, go for the punish. The trap is a big investment of tempo, and we’re likely suboptimally if we don’t get our value from it. For Smelt in particular, we have lots of cheap ways to answer threats, and (unless you are worried about a huge buff like Aegis) a full clear may not be necessary. With the resources you have left after the punish, I recommend defaulting towards board control and eliminating the largest threat. If the trap is a one-off, like Fox Familiar, begin setting up your next trap to carry the momentum. If it’s a repeated trap, such as Griff Scout, keeping it alive presents a great threat to your opponents, and can force them to use their answers in very unhelpful ways.
Because I just spent ~ 700 words talking about vague theories of card value, here’s some more concrete examples of traps you can set up with Smelt.