Need advice to counter Mesmers
Which specific clone is giving you trouble?
If it is the face melting illusions that are giving you trouble, I recommend DPS’ing them down quickly. The HP for those illusions (called phantasms) are very low, and only 2-3 hits should take them down. Then I would recommend putting pressure on the mesmer (there are several other threads that focus on how to recognize the correct mesmer through the clones).
Also, try to recognize the different types of phantasms. They all react differently. For example, the warden is the phantasm with dual wield axes. That phantasm is rooted in place but will do insane amounts of AoE damage. Best strat is to roll away. He will not follow. Another phantasm is the berserker. This one will follow and do a spin attack which will cripple you. DPS this one down quick (HP for this phantasm is very low).
Don’t use projectiles, bring AOE. This will probably help you in fights against any mesmer and their clones. Ground targetted aoe can’t be reflected, clones won’t run out of it, and it just melts them. It’s pretty much the bane of the mesmer’s existence. Besides that any projectiles you use will be thrown back at you. AOE and melee is your saving grace. Watch for confusion if you can too. It doesn’t hit as hard as it does in PVE but if you’re using a fast-hitting melee weapon it’ll start to hurt quickly.