This card feels very underwhelming in solo. However, it's a MASSIVE defense option for higher count games. The card redirects a villain attack, regardless if your hero is ready and that is absolutely amazing. Imagine this scenario in a 3-player game:

The defending player is first. They can either defend for themselves, or take a hit and hopefully defend for the second player in the round. They can use various ready-effects, some of which conditional and risky, such as Desperate Defense. Now enter "I Can Do This All Day". They can just play it at any time they desire, with full control over redirecting the attack and taking advantage of their DEF, all the while not having to be ready for this to occur. Normally, you could only do this with Preemptive Strike.

The card is zero effort required to take full advantage of your DEF stat. It literally reads "take an attack and reduce the damage by your DEF (which should be at least 3-5 in Protection)". No perfect defense required, player order doesn't matter, just pure defense for those who take the role seriously and buff their stat. A ready effect without the ready effect, for the purposes of defending.

It's an amazing deal for defending heroes in high player count games and probably an insignificant card for those playing solo.

This bad boy on a Jessica Drew / Spider-Woman (Hero) deck, can loop with himself and Rapid Response for 2ER. Then we have him for 4-THW, or for 2-THW plus a villain Block.

And the second best part of the loop is that he can actually tutor his Rapid Response when you first play him.

Oh, and he will also secure Sky-Destroyer's activation, every turn.

Coup de Grâce is one of those cards that can do wonders when you build around it with a specific hero in mind, or is completely unplayable if you don't. It's obviously not a card that you'd include in any Aggression deck, or even a card you would consider 95% of the time.

When do you want to work with it? For starters, you absolutely need a reliable way to attach upgrades to minions. Valkyrie, Cyclops, Rogue and Tigra are probably your best bet, as in these heroes have a built-in mechanic that attaches upgrades to minions. There are others as well, but with some of them you need to go out of your way to do so, and it doesn't seem worth it. For example, I don't consider Iceman's Frostbite particularly good against minions and wouldn't focus on it.

Even if you are with the right hero, you may have to include a specific package of cards that works with Coup de Grâce - in particular, any combination of Air Cover, Suppressing Fire and Marked. The goal is to make attaching upgrades to minions easy and 100% independent on card draws. You can also consider some of the cards that bring minions out of hiding - Angela, Face the Past, Looking for Trouble and Spoiling for a Fight. Air Cover in particular works very well for Coup de Grâce, along with Marked/Suppressing Fire.

If you are with the right hero and/or cards that go along, the attack event has 2 notable benefits. First, cancelling bad 'When defeated' abilities can be very good and can save you a lot of trouble. For example, I think cancelling each of the minions that come with the same box Spectrum, Black Panther, Goliath, Hercules and Falcon to be very beneficial. Of course, that's the upper end of the benefit, with the lowest one sitting at not cancelling any ability and just using the card to dispatch the minion in one go. But that is the second benefit of the card, and it too can be a good one. You have to remember that sometimes minions have very nasty abilities (refer to the list in the other review) or a high enough HP value that makes it difficult to damage them. Sometimes minions cannot even take damage, but they can be dispatched with Coup de Grâce. Why go through trouble to damage and kill a minion, when Coup de Grâce can just one-shot it for you?

The limitations of the card lie with the fact you have to spend an extra card in the form of an upgrade to attach to the minion. This can sometimes net you other benefits, such as 2 heal from Suppressing Fire, but it does mean that you are ultimately paying one extra card for the event, effectively bumping the 2 cost to 3. Another negative is that you may not always have an upgrade in hand, in which case Coup de Grâce cannot be used. Couple that with the fact that some minions need to be removed asap, and you are left in a situation where you cannot rely on an otherwise easy removal. Also, obviously, it only deals with non-elite minions, which is something to keep in mind, as it can be overlooked.

To summarize Coup de Grâce

• Good: Deals with very nasty abilities
• Good: Is an attack, with all of the benefits that come from it (pay for it with Martial Prowess, heal from Suppressing Fire, etc.
• Mix: Works with certain heroes only
• Mix: Works well only when you lean on synergies with it
• Bad: Can be extremely situational
• Bad: Depends 100% on other cards to work at all
• Bad: Only works on non-elite minions

Im surprised that he isnt reviewed yet.

• He is an expensive 5-ER card that is restricted to minion/side sch
• Can flex a sum of 6x between THW and ATK over two turns, plus a chump block (not worth imo)
• Can flex a sum of 9x between THW and ATK over three turns (last 3x instance is unrestricted). Decent for his cost imo.
• Maria Hill (Hero) + Field Agent or Med Team can make him stay longer. Though he is a direct competitor of Dum Dum Dugan, I think both can coexist for a great overall table pressence
• In minor effects, we have him as AERIAL trait for tribal decks and for Eyes in the Sky
• Other minor effect if that he brings the exclusive EXCALIBUR trait for multiplayer Strength in Diversity plays
• In a very unreal, voltron-gunboat deck, we can have him Honorary X-Men + Mission Training to add 4x to the sum of Gunboat Diplomacy
• In a multi-aspect hero (Warlock, Spider-Woman), can be affected by or combined with: Flying Formation, Aero, Cloud 9, Air Supremacy, Bombs Away, Aerial Intervention and Wingman

• Already mentioned (by @alatreon): Ms Marvel's (Hero) "recur" feature plus her Biokinetic Polymer Suit + Shrink; increases its maximum THW by 2x3 (+6, a total of 12 THW)

• Jubilee (Hero), where Three Steps Ahead was first released, not only have a suited kit for mix, but her Jubilee's Coat adds an extra instance of 3 THW (A total of 9 THW) for a scheme that you choose (can even be a different, 4th scheme)

• Other cards can combine with said characters' kit and increase the instances by 1x3 (+3 at its maximum): Operative Skill, Passion for Justice (by @waltercardcollector)

While its cost is expensive and you have to build around the card in order to maximize its effects, the built-in ability to distribute three instances of 2 THW gives a flexibility that very other few cards have (All-Points Bulletin, Gunboat Diplomacy). In resume, this card will dominate as central key of decks that will become based around using it.