User blog comment:SolZen321/The biggest Grammatical Mistakes/@comment-1030114-20160321075236

'But' can start a sentence, but it is used so commonly in fiction that it seems out of place, and is rather difficult to put into correct grammar.

Phrases such as "But, even with the assistance of the Ultra Brothers, Tyrant seemed to be undefeatable" are grammatically correct, but they do fall a little bit on the flowery side, if you know what I mean.