Need help with a few template questions

[CyberThread]

what are the two templates that deal with merging two creatures together, and one that deals with having two heads?

Are either of them any good for a player to use?

[Zanos]

Tauric, Symbiotic, and Multiheaded.

All three are in savage species. Symbiotic have the mental scores of the guest, which has to two size categories below the host.

They have potential applications, but I've never used them myself.

[Urpriest]

Symbiotic and Tauric are "good" for a player to use in that they officially ignore the LA on one of the creatures combined, which makes them brokenly powerful when that fact is exploited. Dread Blossom Swarm Symbiotes and hideously template-stacked Tauric creatures are two options frequently bantered around.

Multiheaded is a bunch of LA and some RHD for not all that much PC benefit. That said, it uses the old version of Lernaen Hydra, where you actually have to sever the head to kill it. That should be updated to the 3.5 version, but if unupdated it's a great way to make an unkillable character when combined with something that can't get its head cut off like a Lumi.

[gurgleflep]

For combining two critters together, there's the amalgram template from Green Ronin publishing's Advanced Bestiary if I remember correctly. I' e only used it a handful of times but it's pretty dang cool :D