There are 2 types of tactic cards: Double Shot & Artifact.
Double Shot Cards
Double Shot cards were released in the following expansions: Classic, Monumental, and JLA. They represent two teammates working together with 2 cards to make a single attack or defense. Doubleshot cards have a power type and value required for a specific character to use. They act as a certain level and type power card for the character using it. There is a requirement that a teammate must contribute a specified type of power card.
Below are some examples of pics.
Artifact cards are great additions to any deck. Once played, they can permanently affect one of your characters, your entire team, or even the very mechanics of the game! For instance, you can permanently increase a characters strength rating to 7, while another artifact allows you and your opponent the option of drawing 6, 8, or 10 cards each battle.
There are only 16 artifacts in the game. Below are some pictures of a few of them.