As you can see, theres a lot of good reasons to go and build an almighty Hydra deck, so we reckon you should just go ahead and do it
Even so, it is a huge swing when it happens and that is generally up to you
Giving your team hexproof is a great roadblock for your opponents since they need two pieces of interaction to kill anything that's not Sigarda, but the card advantage is what you want
You may move a Character to a Location on the same turn its played, and it doesnt matter if its exerted or not
Force an attack Another way blue can deal with a creature is to force it to attack into something that will block and kill it
In general, I would look at these two factors when looking to include cards not of your tribe's creature type: Is this creature so strong that it, on its own, is generally stronger than my tribal creatures when they are receiving bonuses and/or empowering my other cards