From Brotato Wiki
Landmines is an in-game item that can be bought from Shop or can be found in a Crate. Most Items increase the Stats of the player while some of them provide unique effects.
Buying the item spawns 1 Landmine at the beginning of each wave and every 12 seconds during the wave. The mine explodes when enemies step off the mine dealing 10 + (100% ) damage to enemies in an area.
Screwdriver spawns the same Landmines, but with different cooldown depending on the tier of the Screwdriver.
Landmines are unaffected by Primary Stats, such as Damage, Life Steal, Attack Speed, Crit Chance. But is affected by Engineering.
Landmines are affected by Secondary Stats such as Explosion Damage and Size granted by Dynamite & Plastic Explosive.