I don't doubt it's fun.But sadly sinister, as many characters, is awful on AI's hands. He is not fool proof like colossus or SW. Also his traps tend to stale the board. With SC or sersi that problem is solved and then is pretty fun, still they will be awful on defense.I think elektra will perform way better with a special tiles buffer instead of him, or a charater giving special tiles like colossus, enhancing a third of her toolkit.
His trap tile triggers regardless of who matches it. When I was using Sinister, I didn't chase his trap tiles too because Behold will deal the maximum damage more easily. The other weakness of his trap tiles are they don't trigger if destroyed by match-4.His boosted Behold, with 8 friendly trap tiles on board, deals ~67,900 damage, which is about 1/3 of boosted 5* health.Anyway, trap tile based characters are not a popular choice for some reason. I guess it's due to to traps dealing low to mid damage.