Death Prophet + Shadow Shaman

Why this works

Pushing down a lane with both ultimates available creates immense pressure. Shadow Shaman can lock a target down with Shackles, letting Death Prophet drain them with Spirit Siphon and get her ghosts rolling. The issue is redundancy. Both Exorcism and Mass Serpent Ward are premier tower-destroying spells. While having both makes taking an objective very secure, you're often committing two massive cooldowns for a single building that one of them could have handled alone. They're both trying to accomplish the same goal rather than covering each other's weaknesses.

The game plan becomes very straightforward: use Shaman's disables to secure a kill, then drop both ultimates and melt a tower before the enemy can respond. This can snowball a lead effectively. The downside is predictability. If the initial gank fails or the enemy team has good waveclear and disengage, you've spent two of your most important spells for little gain. The opponent's strategy is to survive that one big push timing and then punish the long cooldowns, which often resets the game's tempo back to neutral.