Belt of Reduce Person

[blargney the second]

You could delve into psionics: Compression - Pathfinder_OGC

 

[milo]

Alter Self lets you take the form of any medium or small humanoid and doesn't have a restriction on creature type.

 

[hornedturtle]

I thought you could cast enlarge/reduce person on a Eidolon.

 

[SteelDraco]

I thought you could cast enlarge/reduce person on a Eidolon.

Synthesist is different. You explicitly count as whichever's worse for you, so you can't get Enlarge Person while fused. The Share Spells eidolon ability does normally let Enlarge Person work.

 

[hornedturtle]

Nowhere on the Synthesist page does it actually say that you loose the share spells ability, just that you can't target the summoner and eidolon separately. I would think that that means that both you and and the eidolon are targeted and that only the eidolon would be enlarged. That might mean only if the spell is cast by the summoner, meaning that a generic belt wouldn't work but maybe one made specially by a summoner would.