Olaf's Attack Speed is increased by 1% for each 1% of his Health he is missing.
1
Undertow
Olaf throws an axe into the ground at a target location, dealing damage to enemies it passes through and slowing their Movement Speed. If Olaf picks up the axe, the ability's cooldown is reduced by 4.5 seconds.
2
Vicious Strikes
Olaf's Attack Speed is increased, he gains Physical Vamp and has increased healing from all sources based on how much Health he is missing.
3
Reckless Swing
Olaf dashes to an enemy and attacks with such force that it deals true damage to his target. If the target does not die, Olaf takes true damage.
Ult
Ragnarok
Olaf temporarily becomes immune to disables.
Ability descriptions from the official Wild Rift website.
This page is for League of Legends: Wild Rift (the mobile game), not League of Legends on PC. A Japanese version with guides and matchup notes is available: 日本語版.