"Victory shall be ours, it shall be swift, and it will be honest, purchased with blood."

Legate Lanius, Caesar's Ace

Decimate — When Legate Lanius enters, each opponent sacrifices a tenth of the creatures they control of their choice, rounded up.
Whenever an opponent sacrifices a creature, put a +1/+1 counter on Legate Lanius.

Fallout

Decimate — When Legate Lanius enters the battlefield, each opponent sacrifices a tenth of the creatures they control, rounded up.
Whenever an opponent sacrifices a creature, put a +1/+1 counter on Legate Lanius.

For example, when Legate Lanius's first ability resolves, an opponent who controls between one and ten creatures will sacrifice one creature. An opponent who controls between eleven and twenty creatures will sacrifice two creatures, and so on.