Like Super Monkey Storm, the Thunder Druid is a card most useful against large swarms of bloons. Thus, it should be saved for when it is truly necessary. It's more powerful than a single Spike Storm! for anti-aggro against groups, but much more expensive. It provides better burst damage against a single Bloon with its attack.
Since it costs 3 less Gold than Super Monkey Storm, it can be played on turn 3 if the player saves all their Gold and is going second.
Unlike other board clears, Thunder Druid has other potential uses after being played, due to it being a Monkey:
The initial attack from Thunder Druid causes it to deal the most damage to a single target out of any field clear, with it doing a total of 180 damage in comparison to Super Monkey Storm's 150.
Adora can use Ultimate Sacrifice on a Thunder Druid if not planning to re-use it.
Return to Sender or Adora's Salvation can let the player reuse the on play effect, if needed for another use of the on play effect.
Clever Bloons (e.g. Clever Yellow Bloon) can be played afterwards to trigger their Clever effects.
Thunder Druid can be useful in decks that want a mix of single target and AOE damage in one. The massive burst damage makes it easy to justify running Thunder Druid in decks with heroes like Adora, as she prefers Thunder being a Monkey for sacrifices or Salvation.
Reworked animation for Thunder Druid. Now slowly looks at the sky with its wand and strikes lightning from above, instead of aiming at bloons and forking lightning across.
The flavor text for Thunder Druid translates roughly the same in all languages except English. The other versions translate loosely to "Did someone ask for THUNDER?"