Assassination cards are ones that allow you, the offensive player, to pick one of your opponent's character cards and take them to KO/prep, or to the used pile. It's as simple as that. When you attack, your opponent gets to choose how to block, so that 8A/8D Hulk isn't worth much if your opponent can just use a puny sidekick to distract Hulk. (Obviously the addition of an Action like Throw Car will change this, but we're speaking in general terms). When assassinating, you get to pick who goes down, and ideally you don't give your opponent a choice about it.

Fair Weather Assassins

There are a few cards out there that do not automatically get you that assassination, but give you good odds. These guys aren't always cheaper, but they usually have a little something extra to sweeten the pot on using them.

My favorite occasional assassin is Storm. Every form but her 2 cost 'Ro' form offer you the opportunity to pick some of your opponent's dice and force him or her to reroll those dice. If the dice are no longer showing a character face, they go either to prep or to your opponent's used pile. Her Wind Rider form even has the benefit of letting you pick two, sending them to the used pile, and doing two damage to your opponent for each character killed this way. Fantastic! Her Goddess of the Plains form is also very effective against Gobby decks because she's very likely to KO most, if not all, of your opponent's sidekicks, and it's not that easy to get them back out. She's dangerous in a lot of other circumstances, though, because she sets your opponent up to have big energy hands the next turn.

Another two fair weather assassins are Hulk: Jade Giant, and the Basic Action: Smash! Jade Giant (or you) have to be damaged to get his ability to happen, but he'll KO either a level one character (if Hulk is on his level 3 side) or a character of any level if he's level 1 or 2. Similarly, the Smash! card lets you KO one level 1 character, or a level 1 or 2 character on its burst faces. They are both situational, but they can get the job done on many of the cards your opponent could have out there.

Hulk isn't a particularly cheap card, but Smash! clocks in at 3 energy, and Storm you can get for anywhere from 3 to 5 mask energy, so both of them are relatively cheap. Storm: Goddess of the Plains loses some of her utility later in the game if your opponent has out several characters, but African Priestess and Wind Rider are going to be very useful throughout the length of your game. If you bring GotP, make sure you buy her early, because her utility drops precipitously if your opponent gets out about 4 or more characters that aren't sidekicks.

Storm is really a character you're going to be using for her ability; she's never going to bring much hurt to your opponent, sadly, due to her smaller attack. Hulk, however, is pretty great on the damage front, and he's a beefy blocker if you need that, so his 6 cost at least gets you an extra nice guy on your field.

Edit: I missed a pair of fair weather assassins in my first writing. The first is Hawkeye: Longbow, at 4 bolt energy. He's a bit situational, unfortunately, because he deals his attack to a character when he's fielded, but he only has 3-4 attack, which means he'll be able to assassinate the smaller characters, but will be useless against some of the tough guys like Loki, Doom, or high level Venoms, who can all really hamper your day. Still, he is worth noting, and if you manage to bring out two in a turn you can kill pretty much anything on the table. I think he's fantastic as a supplement, but I don't really feel like he can hold his own as your only assassin on the field. It's a personal preference, however, and if your team is fast enough it's unlikely you'll ever need to assassinate a heavier hitter. It's definitely a thing to think about when considering your assassin options.

The second is even more difficult to pull off. War Machine: James Rhodes will knock out an opponent's character when fielded, if you have Iron Man fielded. I don't think I have to say how difficult it can be to pull off this combination. You have to bring an Iron Man, and he's not cheap; he costs 4-6 shield energy to buy, and then another 1-2 to field, while War Machine costs 5 to buy and 1-2 to field. Keeping characters on the field can be difficult depending on what sort of assassination options your opponent brought, or even if he or she is just keeping the pressure on. I don't really consider him a valid assassination option, due to the fact that he's completely reliant on Iron Man for his cool stuff. Honestly, I dislike that about all of the War Machine variants, but that's a thought for another time.

Finally, there are the Stone Cold Killers; these are characters who will just flat out murder a guy. I love 'em. My favorite is Punisher: McRook. He's fairly cheap, at only 4 energy, so you can buy him on turn one if that strikes your fancy. When he attacks, you get to pick a character to KO. Your opponent can prevent this by taking two damage, but Punisher is still coming at your opponent for 4-6 damage that needs to be handled. McRook is a fantastic character, with some of the best stats in the game for his cost; he's also fairly cheap to field, at only TFC 4 with an expected cost to field of about 1ish. Cheap to buy, and not too expensive to get out makes him a very solid early buy. He doesn't have quite the versatility of Storm, but he also puts you at much less of a disadvantage if your opponent's rolls and rerolls don't go your way. He's also a common, which is just incredible, so you really should have him as an option in most decks if you want him. 

Moving up in cost just slightly we have Deadpool: Jack. He costs 5 fist energy, is very cheap to field at TFC 1 with an expected field cost of 0ish. When he attacks, you can assign a character to block him, and at the end of your turn, you KO that character. Deadpool also has fairly solid defensive stats (4/5/7), so the chances he actually survives this assault aren't insignificant. He's pretty great, actually, but his offensive stats (2/2/3) are mediocre so he's not going to be KOing many people just on the strength of his own stats, and he's not going to be putting loads of hurt on your opponent either.

The king of assassins - at least when it comes to damage dealt and chaos wrought - is Loki: Illusionist. He costs a whopping 7 mask energy, but when he's fielded he takes control of an opposing character (which means you can attack with that character if you want), and at the end of your turn he KOs the controlled character and deals damage to your opponent equal to the captured die's attack power. Nice! I'm not sure he's going to be your choice of an include over Loki: Gem Keeper, but he's a very effective assassin for his price, and he's going to put a serious dent in your opponent's defensive strategy if you yoink his or her Hulk (or other heavy hitter) and send a good 6-8 direct damage at him or her.

So which of these lovely assassins should you be looking at for your deck? It depends! Some of them (McRook, Goddess of the Plains, and Deadpool) require you to attack. Sometimes you don't want to do this! Maybe they have out a Beast: Genetic Expert and you don't want to give your opponent the chance to block with him even if they aren't level 1. Maybe you have a Wolverine as part of your offensive strategy, and you want/need him to be attacking solo. Maybe you really want to use Deadpool for his defensive stats because your opponent has Throw Car and you want to make sure you can soak the damage with his beefy defensive stats. There are a lot of reasons you might not want to include characters that require you to attack.

One nice thing, I'll point out, is the Global Ability on the Distraction Basic Action does allow you to retreat an attacking character for 1 mask energy. 'When this character attacks' abilities assign when the attack is declared, so you can attack, and retreat, if that's what you need to do. (This is also a great way to tweak a Tsarina blitz if you want to, dealing that 2 damage or spinning a character down, but then pulling her back so she doesn't get KO'd).

Some of these, like African Priestess and Wind Rider go when a character is fielded which means that you can use them even against something like Doom or Venom who would KO your character the second they hit the field. On Field effects are a little tricky, however, because your opponent could try to keep the character out, making sure you can't field it again quickly rather than KOing it for you.

Smash! is also an option, but I'd personally never leave it as your only option, I just mentioned it for completion's sake.

My favorites are definitely Punisher: McRook, and any flavor of Storm (although African Priestess is my favorite with Wind Rider as a close second. Goddess of the Plains is a bit too much of a double edged sword for me). Ultimately, it depends on the sort of deck you want to put together, but these assassin cards are an archetype you want to think about when constructing your deck. Even if you don't include one, you're going to face one.

Roll on, and I'll see you next time.