I must admit I rarely use Grumpy with my regular accounts. Fire has Giant Roc, Death Has the wolf, Earth has the Minotaur and Life has the Silvershield Warrior. But not having the means to get all of them at a decent level, required a different approach. I would have never thought of Grumpy if @bashadow hadn't mentioned him.
Although I've been playing for months, it wasn't until about a week or two ago that I finally understood how the sneak ability really worked. So now I set up my team with a tank in front, if there is enough mana, a monster with reach in second - if there's not, I leave it out - and then a magic or range 'buffer' that can take some hits to protect my tank healer from being taken out too quickly.
It's hard to imagine I was able to reach champion a couple of seasons ago with my level 6 deck without understanding that sneak monsters go for the first range or magic monster in the lineup, lol.
I should look into those neutral monsters a little more. The Centaur, for example, I've been using quite frequently when playing my other decks. Those neutrals can indeed be used with all splinters, which makes them very useful. Unfortunately, compared to the other betas, they're quite expensive.
the grumpy dwarf only costs 4 mana making it more economical than the roc/wolf anyways. The centaur is also very good. creeping ooze and cocatrice come in handy sometimes aswell.