Ogre

The Ogre is one swing that ends a level 1 character

How to run it. 68 Hit Points, AC 11, Speed 40, and one attack a turn: a Greatclub at +6 for 2d8 + 4, or a Javelin at +6 for 2d6 + 4 out to 120 feet. No multiattack, no tricks. It is CR 2, and the whole threat is the size of one hit.

How hard it hits. A level 1 fighter with 12 Hit Points drops to one Greatclub hit 67% of the time. A level 1 wizard with 8 drops 95% of the time. Against AC 16 it hits 55% of the time; against AC 12, 75%. So for a new party, the Ogre is a coin flip on losing someone every turn it swings at the wrong person.

The choice that matters is who it swings at. With Intelligence 5 it won't think tactically. Have it hit whatever hurt it last, or whatever looks smallest. Tell the table which, through what it does.

The common mistake is running it as a punching bag because its AC is 11. Players hit it 75% of the time at +5, and 68 Hit Points still take a new party three or four rounds. That is three or four swings from the Ogre.

For players. Its mind is the weak side: at Wisdom −2 it fails a DC 13 Wisdom save 70% of the time. Keep it from closing, but kiting has limits: Speed 40 catches most characters, and a javelin reaches 120 feet. Spread out so one swing finds one target.

The human angle. One big hit sticks in memory in a way twenty small ones don't. Baumeister and colleagues reviewed decades of research and found bad events outweigh good ones of the same size, in memory, emotion and learning. The Ogre is built for that. Players forget the misses; they remember the swing that dropped the cleric.

Source: Baumeister, R. F., Bratslavsky, E., Finkenauer, C., & Vohs, K. D. (2001). Bad is stronger than good. Review of General Psychology, 5(4), 323–370. doi:10.1037/1089-2680.5.4.323