Hello,
if a spellcaster with an animal companion casts a spell affecting only the spellcaster, is it possible to share the effect of the spell with the animal companion.
Or are there means for a spellcaster to merge with an animal companion ?
Thanks for your future help.
1. No, spells that affect you don't affect a companion.
2. Also no, your companion can't be made a part of you.
There are some spells that target your animal companion specifically. I don't recommend Final Sacrifice as one of them, but it is available.
You can also cast most other spells on an animal companion if they can also target your allies. You just can't cast self-targeting spells on someone else - including your companions.
As for merging, I am not aware of anything like that for animal companions or other similar companion types. Familiar and Eidolon only.