You can use ANY weapon (doesn't have to be [Tekko]).

The best option with or without a riven is [Tenet Agendus], [Tenet Exec] or [Kuva Shildeg] with +60% toxin. Do NOT use [Tenet Grigori] or [Tenet Livia] as their passive prevents combo gain. Second best options are high disposition weapons with a good riven eg [Amphis], [Ankyros], [Ether Daggers].

Ideally you want Arcane Avenger on Atlas, but even without avenger, crits are viable.

Total +Dmg = 265% (multiplies base dmg by 3.65x)
Total +Elemental/impact = 345% (multiplies base dmg by 4.45x)
Total +Crit Damage = 150% = (5x final Landslide CD)
Total +Crit Chance = 550% (32.5% final Landslide CC or 77.5% after arcane avenger)

Riven :
Best rolls: Damage / Crit Damage / Elemental or Impact

Replace [North Wind] or [Spoiled Strike] with riven depending on the final dmg to elemental balance
e.g. if riven adds +200 dmg and zero elemental and you replace [North Wind], then final dmg will be 465% and final elemental will be only +255. This is 'unbalanced' meaning stacking into dmg creates diminished returns, with a final damage multiplier value of 5.65 x 3.55 = 20.06x. If instead you replace [Spoiled Strike], final dmg will be 365% and final elemental will be 345%. This is more 'balanced' and will create a slightly higher final multiplier of 4.65 x 4.45 = 20.7x.