Early game · first 8 minutes
Keep solid cover between you and Sinclair’s Vexing Bolt. Destroy Spectral Assistant when you can do so without taking fire from Sinclair.
Rat King vs Sinclair
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Mid game · Walkers
Spread out so Rabbit Hex cannot catch several teammates. Use Royal Pestments before Sinclair reaches you with the hex, while you can still cast it.
Late game · Patron
Watch Spectral Assistant during a banner push; Sinclair can swap to its position. If he swaps, send rats at his new position and follow with gunfire.