How can i do to set a player in fire ? To modifying an entity ?

Plugins Plugin Development
1

Everything is in the title. x)
For the entities, how can i modify the “goal” of an entity ? Like the PathfinderGoals in Bukkit.

2 
player.offer(Keys.FIRE_TICKS, ???);

agent.setTarget(???);
3

That’s waht i needed, thx ^^