Sheildbreaker's Bow
Recipe: Last Whisper + Pickaxe + 200G (2375G total)
Stats: +50 AD Unique:+35% bonus armor penetration Unique: +10% auto attack damage on shielded targets
Staff of the Merciless
Recipe: Void staff + needlessly large rod+ 100G (4000G total)
Stats: +140 AP Unique: Ignore 35% of magic resistance. This increases to 45% when applied a champion afflicted by hard Crowd Control
The first one doesn't make sense. Why would you need to do more damage to an ally with a shield? And the second item is too expensive.
I like the intent behind both of these quite a bit.
That said, I feel like the former isn't unique enough -- that passive is even more niche than the existing armor penetration items, and could stand to be expanded upon a bit more if it's going to remain that niche. You effectively lose the entire passive once the shield falls, and often shields aren't big enough to survive a crit from a late-game AD carry, so it's really hyper-specific.
The latter is probably a bit too expensive, and a bit too strong. Void Staff is already an end-tier item, and building something out of it feels wrong. Might be more interesting if it provided less penetration than Void Staff, but jumped up to provide far more against CC'd targets, since that gives you more choice in how you wish to play and what your team excels at.
