Super power: how to beat someone who can absorb a direct attack & reflect it back.?

define "absorb." Would that mean an attack that would be poisonous would have no effect on them if absorbed or you took advantage of the absorption by making them absorb something that will cause damage. If their ability has no specific definition, be funny about it and use an attack that makes them absorb you entirely and kill them from the inside. Such as squeezing them to death, you get absorbed in the process and kill them once inside.

 If by absorb you mean a sponge for direct damage, the only other way would obviously be indirect damage. Such as environmental destruction that damages the person in the process. 

Well, don't attack him directly?

I mean, you can use items/stuffs to attack him, like using boulders/stones, or something like a bomb/explosive, since he definitely can't absorb that.

You could also use AoE magic, and aimed on the ground/area near him. Since his ability only applies on direct attack, he can't do anything if the magic isn't directly targeted towards him, as he can't reflect splash damage.

Another "cheap" method is by using stuffs from nature like forcing him to fall from extreme height, drown/suffocate him in water, using snow/rock avalanche to crush him, or using something like a mass-plague/curse.