Maarika, Brutal Gladiator must be blocked if able.
As long as it's your turn, Maarika, Brutal Gladiator has
indestructible (Effects that say "destroy" don't destroy that permanent. An indestructible creature can't be destroyed by damage.).
Whenever Maarika, Brutal Gladiator deals damage to a creature, if that creature was dealt excess damage this turn, that creature's controller sacrifices a noncreature, nonland permanent.