Dummy

The Dummy is the first "enemy" encountered in the game. It serves as the game's tutorial enemy.

Strategy
Are you really asking what the strategy is? The thing can't do anything, just attack.

Hard mode
It is literally the same strategy as a normal Ice Spike. Which means it can pose a threat if you are low-leveled.

Trivia

 * The Dummy never disappears, even if you beat it up a lot of times.
 * This makes it a very easy way to grind Exp. Points, though not very efficient.
 * The fact the Dummy has a soul in it is a reference to Undertale's own Dummy, which is possessed by a ghost.
 * Due to the tutorial, the Dummy's Memory Hall entry is automatically unlocked when Tower Town is reached.