Anime - Boy with a gem on his forehead could transform and combine, as could a cat and another person [duplicate]

Question

I'm 16 and when I was 6 (around 2006-2007), I used to watch a cool anime (don't ask me what channel because i found out it was illegally downloaded by my other friends).

I only vividly remember certain aspects of what it was like. I think there was a boy with maybe some kind of gem that I think he wore on his forehead, and he could transform into a grown man (again, I think so). Then there was a fat cat who also had a gem; he could transform into a tiger. I think there was a third person where, all together, they combine and make one powerful grown man. It's been bugging me since I was 11.

Answer 1

Could you be thinking of Shinzo (or Mushrambo in the Japanese version)?

From Wikipedia

Shinzo, known as Mushrambo (マシュランボー Mashuranbō?) in Japan, is an anime television series produced by Toei Animation. In the series, genetically-altered creatures known as Enterrans take over Earth and rename it in their own image called Enterra. Now three Enterrans have to protect the last human in order to find the hidden sanctuary called Shinzo and restore the human race. The anime focuses primarily on the adventures they undergo while working to accomplish this task.

Mushra, Sago. and Kutal are then shown to be Hyper-Enterrans, Enterrans who can transform into stronger powered-up versions of themselves, these forms allow them to fight the various creatures that come after them.

By absorbing Hyper Sago and Hyper Kutal's EnCards, Hyper Musha becomes the reborn Ultimate Warrior of Enterra

Here are the three main characters and their transformed versions

And their combined form, Mushrambo