The Diamond is a monster encountered in Dark Cloud and Dark Cloud 2 that is classified under the Card type. All variations of the Diamond behave in exactly the same manner. In Dark Cloud 2, if you throw a Gift Capsule with 3 Diamonds at a Diamond monster or any of its variations, you'll get the Card Monster Badge.
The Diamond and its variations wield a spear, guarding will reduce damage, but not by much, as the card can go around your defenses. It has no other attacks but a single tackle. This enemy boasts a moderate attack power but as said its deadly characteristic is it's ability to pierce the player's defense and cause knockdown regardless of the player's block. Though very dangerous in close quarters, Diamonds can be taken down easily if the proper fighting strategy is used. The best of these are:
Hit and run, the best used tactic for most if not all enemies in Dark Cloud, done by simply 'hitting and running', attacking three or four times, then moving away and repeating the process.
Attacking from a distance, in Dark Cloud 2, using either ranged weapon attacks, or lightning stones. The first method isn't the most efficient way, as these monsters have the ability to guard against attacks. The second is a one hit kill: but lightning stones are scarce so it is only recommended when you have more than ten stones (Stones are usually saved for use against windups)
All in, the method used in Dark Cloud 2, comprising of a few ranged attacks followed by a stream of melee attacks, downing the enemy forcing them to get up, then using ranged attacks until the target is almost up, than followed by more melee attacks and so on. In almost every one-on-one situation against downable enemies this tactic rules over almost all others in effectiveness, and has no substitute in efficiency (Done right, you will have no need to heal or use any assist items besides Repair Powders).