The strategy of this deck is simple against aggro, just do whatever you can, this deck is not strong against aggro so use what you can when you can to survive.
For a more stable version of this build check out the taunt version I made which still keeps the combo package while ensuring it doesn’t just die to aggro. http://www.hearthstonetopdecks.com/decks/taunt-recruit-druid-with-combo-package/
Now against late/midgame decks this deck becomes much more interesting, you have a few “combos” in this deck, most revolving around Umbra. The first one and the one you will be doing regularly is to play Umbra
into Witching Hour after one of your Grizzled has died, this causes you to instantly get your 2 tigers (hopefully) that then also get new
copies into your deck which can be pulled when your guardian dies, this also leaves enough mana to play a baleful banker on umbra if you are up against slower decks where you can pull of several combos.
Second major combo is if
you are so lucky that umbra stays on the board or is pulled by your
guardian, then you can play witching hour plus cube to get a very over
saturated board. (umbra, cube, tiger, tiger, guardian, guardian, tiger, +3 tigers that can’t be spawned)
This is far from all the combos but the others are fairly obvious, like Umbra into Cubing Hadronox if the opponents doesn’t want to kill it. Or Umbra into Faceless a Cube/Guardian/Hadronox which triggers said deathrattle.
Now some might say to replace Bewtichet Guardian with Witchwood grizzly, but this deck really wants to make sure you get exactly Grizzled Guardian from your Witching Hours. If aggro decks become overly common you might do something like that though just to have a better chance of surviving them and just leave the grizzly as a dead card until you play both Witching against slow decks.