The subspecies found in north-east Brazil, S. b. gracilis, looks similar to the nominate race though it is slightly smaller. Note the broad yellow supercilium, the large pale patch on the wings and the white tips to the tail.

This area of north-east Brazil is the only place where the Greater Wagtail-tyrant is sympatric with the very similar Lesser Wagtail-tyrant, Stigmatura napensis. At one site where they can be seen together, the Lesser can be seen to be smaller and it also forages lower down than the Greater Wagtail-tyrant.

Ridgely & Tudor state "despite the bird's name, its tail is never exactly wagged" but, as you can detect in the second photo, it can cock its tail quite rapidly.