Menno Coehoorn is a close combat card in the Nilfgaardian Empire deck.
Card is on of those strongest cards in the game. Not only it has a strength of 10 and is a hero card (making it unaffected by weather cards) but it is also a medic, making it superior to most heroes in the game, and one of the only medic heroes, the other being the weaker Yennefer card (strength of 7).
Arguably, it may considered be even stronger than the Geralt and Ciri cards, whom 5 extra combat strength is often less important than the medic ability, able to bring back stronger units or a spy. However, you are likely not to have to choose between these cards and simply put all of them in your Nilfgaard deck.
Being a medic, playing it without any good "dead" card is wasteful. One should wait until the second round to play it unless a powerful and needed unit has been destroyed during the first round. Also, being a hero he can not be called back by another medic or by a decoy card.