The Li'l Murderer, also known as the Tricker, is an enemy from Final Fantasy IV.
Li'l Murderer has the Float effect and uses Scan on itself to reveal its weakness to Lightning to the party, but this is a trap—attacking it with any form of electrical ability causes it to retaliate with powerful electrical attacks of its own. As long as the party avoids using Lightning attacks, the Li'l Murderer can be beaten easily—it will just keep scanning itself while the player attacks it with physical blows.
If the player does not wish to continually deal with the message that comes along with Scan, it is vulnerable to Stop, which will speed things up a bit. It is also possible to rig the team with Reflect and bait the monster into killing itself. The player can also use it as an opportunity to completely heal the party with Pray without fear of retaliation.
The Li'l Murderer's name in the Easy Type version, Amanojaku, is a small oni in Japanese folklore. It could provoke a person's most evil desires and drive them to do wicked acts. To an extent, this reflects its actions as an enemy, as it "provokes" the party by revealing its weakness to Lightning.