A normal blaze spawner can do that.if a tier 4 can spawn blazes in the overworld, then it should be able to spawn slimes in any biome.
a normal blaze spawner is found in the nether... Although, I've not tried gravity gunning it back to the overworld, I do know however that blaze shard spawners up to lvl 3 will not work in the overworldA normal blaze spawner can do that.
Gravity gunning them works fine. They also spawn the same in the overworld. So really there is no use in using a shard until 4/5; really just 5.a normal blaze spawner is found in the nether... Although, I've not tried gravity gunning it back to the overworld, I do know however that blaze shard spawners up to lvl 3 will not work in the overworld