I often find Brendan acting out fire and rescue scenes on his own. He'll shout "Mummy, turn the water on!" and wait for my invisible double to turn it on before putting out the fire with a belt or a stick. He'll also give orders to invisible Fireman Sam characters and tell Norman and Mandy off for being naughty. He's clearly watching too much Fireman Sam!
But his most interesting imaginary "friend" is his "baby volcano" which he cradles carefully in his hands and then puts down gently before saying "look, my baby volcano is here" which could be on his dinner plate, in a pile of laundry, in the middle of his train set... We watch it erupt and he commentates. There's both "lava" and "molten rock" as well as ash and smoke and sometimes "pizza" (I have no idea about that one).
Speaking of pizzas, at gymnastics we sometimes do a warm up/stretching exercise and when the coach asks Brendan what he would like to put on his pizza he invariably says "a puppy". They say the strangest things sometimes!
His bedtime teddies are more important to him nowadays. Sometimes he'll get up at 3am and come to our bed with his rocket pillow under an arm and three of his soft toys: Robin Bear, Jellycat and Doey. Sometimes he'll also be carrying his Fireman Sam hat too :)