If Lazarus' Rags are used to resurrect, Isaac will only have one heart. This can be detrimental if used with more than one heart container.
Since using Suicide King means death, Isaac will need to have a resurrection item to make a good use of it, such as 1up!, the Ankh, the Dead Cat, or being Lazarus.
When combined with Blank Card and Dead Cat, the card can be used nine times (spawning a total of 90 consumables).
Suicide King won't always drop a pedestal item, but often drops numerous Chests, meaning that using Suicide King on a special room or in Chest/Dark Room can be useful to get good items.
When doing a true co-op run, the player that uses Suicide King can be revived if the other player(s) defeat the floor's boss. An ideal time to use this card would be during the fight with the floor's boss while its health is low. Activating this card right before it is defeated will spawn the pedestal items and allow you the respawn shortly afterward, provided the co-op partners finish off the boss.
Keep in mind that being revived in this way will only leave your character with half a red heart (or half a soul heart if they cannot acquire red hearts) so it may be ideal to let the player with the least amount of health use Suicide King to minimize the drawback.
When Suicide King causes a Game Over (i.e. is used with no revive items), a picture of the last cause of damage will appear on Isaac's last will as the cause of death.
The background color for the Suicide King achievement has the same color as all the Boss Rush unlocks, suggesting that the Suicide King card was originally intended to be unlocked via completing a Boss Rush, with Lazarus.
This is further evidenced by the fact that Missing No., Lazarus's Boss Rush unlock has a Challenge background color. This implies that the Suicide Kingchallenge originally unlocked Missing No., or it was intended to be looked at as an error or a glitch, as Missing No. is a glitch-related item.
The Suicide King is the king of hearts in a standard card deck. It is called this because the character on the card is seemingly thrusting his sword into his own head.
The card quote reinforces the idea proposed by Reddit user Jayborino. That the only way for Isaac to get out of the chest in the "real world", is to die in the game.
This user was praised by Edmund himself for his article being "mind blowingly accurate".