This is a perfect example of a counter deck to this extremely annoying meta that is currently dominating the game. The Valkyrie works very well at countering the witches and wall breakers which both have very high use rates right now. You have two win conditions in this deck, the mortar and the miner. This allows you to apply dual lane pressure throughout the match making it more difficult for your opponent to defend. You have an element of bait inside this hybrid deck, the goblin gang and dart goblin are both log bait cards and allow you to punish the opponent if they use their small spell against one of these cards. Defensive mortars can be important in some matches, especially in single elixir. Against hog rider and bridge spam decks you should focus on defensive mortars and offensive miners. Also against beat down you can use the mortar to kite their tank into the centre of the arena buying you more time to shut down their push. You’re main air defence is the dart goblin, bats and the witch, you also have the knock back effect of the snowball which can work well against balloon.
Miner is a good unit to use to chip away at the opponents towers throughout the match. Make sure you switch up his placement too. Use him aggressively on the counter attack so he can tank tower damage for your counter push units.
As I mentioned above Valkyrie is perfect right now for countering the wall breakers and the witch. She can also beat a mega knight in a 1v1 if your princess towers are helping out. Counter push behind her too and pair her with the miner for extra tower damage.
Dart goblin could be the unsung hero of this meta. His range allows you to defend the opposite range then go on a strong counter push. His speeds allows him to quickly chop through wall breaks, graveyard, swarm units and even the witch (if a unit is tanking damage)
Single elixir you can go in with the miner in the safe spot or even cycle dart goblin at the bridge providing you have witch or bats in cycle. Try to workout what deck the opponent is playing and adjust your play style accordingly. Small chip damage is important to keep up that pressure and force your opponent to spend elixir defensively rather than offensively.
In double elixir you can begin to apply dual lane pressure and build up some stronger counter pushes. Defensive mortars can be used to avoid your opponent rushing opposite lane if you go all in during sudden death. Good luck with this deck!