Sometimes Magic cards interact in ways you wouldn't expect. This is one of those times. It turns out, when you have Brain in the Jar and a card with fuse, you can ramp the artifact to the lower of the two halves of the split card, match converted mana cost with that half, and cast both sides for maximum value.
That means that on your second activation of Brain in the Jar, you can cast both halves of Beck // Call, creating four 1/1 Bird tokens with flying and drawing four cards.
...Ring Ring...Ring Ring…
Hello? Oh, it's the mayor of Value Town, you say? You're resigning your post and in a special election the entire population of the Town wrote my name in? Yes, I can be there next week for the inauguration.
That kind of power makes Lingering Souls, a Modern staple, look like a pile of puke. The price you pay is four total mana between casting Brain in the Jar and activating it twice, and if you have a one-mana spell, you get to recoup a mana from the first activation.
If things don't go according to plan or there is some disaster in Value Town and the people revolt against your benevolent rule, then you get to extract value from Brain in the Jar over the course of a long game with a typical suite of control cards. After the initial investment to get the Brain up and running, you get to double- and triple-spell with ease, allowing you to recoup lost tempo with spells like Supreme Verdict and other removal or simply answering your opponent's threat on the same turn you cast a card draw spell to refuel.
As the game goes long, the second ability on Brain in the Jar becomes quite relevant, allowing you to dig toward a key spell to lock up the game, most likely Beck // Call. You'll want to be careful with your sequencing here, since managing the counters on Brain in the Jar is very important, as is managing the mana you invest into it.
But with some tight play, you have a control deck that can go over the top of every attrition deck or constantly hold up disruption against combo. When it comes down to it, Value Town is a pretty nice place to live.