This looks like a fun idea and is (probably) balanced. It would make for some interesting new scorpion duo decks (dune scorp, deathstalker) as well as enabling certain other sorts, like life/aether fractal spark, or whatever. I have two comments for consideration, though:
1) Does the ability stack? It would likely be too powerful if you could stack these; I'd point to nightfall/eclipse as precedent.
2) Would it be possible to reword the ability slightly? Until I read the notes, I thought that the TIGER was getting the temporary buff when you played other creatures that turn. That would also be an interesting ability, but it's a completely different card. Changing 'it' to 'that creature' would solve my misunderstanding.