Infestation Spawner XP Farm

This one's Bedrock only, built around a potion that doesn't exist on Java. The Potion of Infestation, brewed from a fermented spider eye, replaces any hostile mob it hits (splash, lingering, or on an arrow) with a swarm of several silverfish instead. One mob kill turns into multiple XP-granting kills.

Take any normal spawner room, most commonly zombie or skeleton, sealed and funneled the same way as a standard spawner farm, and add a splash of Infestation to each mob before it reaches the kill point. One spawner-produced mob becomes a handful of low-health silverfish, each still worth its own XP.

Since the potion has to actually land before the mob dies, most designs build a small bottleneck right at the end of the funnel where a player, or a dispenser firing a lingering potion, can reliably tag each mob as it arrives, rather than trying to hit them scattered across a wider room.

Brewing needs a nether wart base potion upgraded with a fermented spider eye, and spider eyes come from spiders, so you'll want a small side supply going (or a trading source) to keep this farm fed. That's a maintenance cost most other XP farms here don't have.

The appeal is pure throughput. Since one zombie spawn can turn into four-plus silverfish kills, this roughly multiplies whatever spawner room you attach it to, without needing to find a rarer or higher-value spawner in the first place.