How to counter Naga Siren

In lane

Axe
• Counter Helix procs after a set number of attacks which is great since Naga Siren is an illusion hero and relies on them in the lane. • Culling Blade gives his allies armor which is great against Naga Siren. It also gives Axe a stacking armor buff for every kill. • If ever Axe catches the real hero and a couple of illusions with Berserker's Call it can be a big problem.

Tidehunter
• The damage block of Kraken Shell works extremely well against illusions. • Anchor Smash is a good spell to deal with illusions since it both damages and reduces their damage. • Tidehunter can buy Aghanim's Scepter to turn Gush into another AoE spell that is good at dealing with illusions.
Timbersaw
• All of Timbersaw's spells are AoE making him good at dealing with illusion heroes. • Timbersaw does not care about illusions hitting him as he has Reactive Armor.

Shiva's Guard
• This is a great item as it provides armor to the wearer and the active helps you deal with illusions.
Mjollnir
• This is a good item to buy to compensate for your lack of AoE damage.