This deck is one of those perfectly awful decks that everyone hates playing against
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The idea behind ash zealot on the sideboard is that if you come up against a similar control deck with few creatures, you will be able to board in the ash zealot, life bane zombie, grey merchant, and duress. You would then board out your creature destruction spells. This makes the deck more versatile in a tournament setting.
Control decks aren't about keeping the pressure on your opponent. They are designed to hold off your opponent until you are able to set up the kill condition
Dispatch sounds good
Love scepter decks, memory lapse is sooo powerful in them, consider...splash black and creature control could work really well, check out my scepter deck and see if it helps. good work.
Awesome combo that is very plausible as a turn 3 kill with more hand control. I would suggest duress or blackmail. Also, counters are very helpful to slow down the game and let you get your combo going. Consider counterspell or memory lapse + scepter turn 2, very powerful. I have a scepter deck that may give you a few ideas, feel free to check it out. Why 75 sideboards?