Magnus + Pangolier

Why this works

Stacking two big teamfight ultimates like Reverse Polarity and Rolling Thunder can be awkward. The core problem is that they achieve similar goals in conflicting ways. Magnus wants to pull everyone into a tight clump and hold them still, but Pangolier wants to be the one moving enemies around, stunning them by rolling them into terrain. If Pangolier starts rolling through the middle of a Reverse Polarity, he can easily push enemies out of the stun duration or away from follow-up cleave damage. The setup from one hero often gets disrupted by the other.

This leaves the team with two initiators who don't combine their best spells very cleanly. Both Magnus and Pangolier need a key timing with items like Blink Dagger to get their fights started, but when they do, their plans can collide. One hero is often forced to hold their ultimate or use it sub-optimally. While Magnus can give Pangolier a nice damage boost with Empower for his Swashbuckle, it doesn't solve the fundamental problem that their teamfight-defining spells work against each other more often than they work together.