I run deck surgery

I plan on replacing some or all of my Demonic Collusions and some of my Diabolic Tutors with Mastermind's Acquisitions (4 of them, though I could do this with only one, we'll see how the price on it goes).

So, what are some fun cards to put in my sideboard? Or useful ones?

Candidates so far:
Followed Footsteps (I have 1) + harabaz for mana
Harabaz Druid (I have 1) + followed for mana
Phage the Untouchable (Win con, but if they get some sort of emblem that says I can't attack...)
Approach of the Second Sun (Win con)
Possessed Portal (Useful vs 200+ card decks)
Praetor's Grasp (Fun)
Pull from Eternity (Useful in niche cases)
Wit's End (Useful vs 200+ card decks to make their hand empty in combination with possessed portal)

What are some fun or useful or very niche cards? Bonus points for being in colors. Note that I am a cheapskate which is why I didn't mention helix pinnacle (costs almost .5 tix)

More stuff:
Ratchet Bomb
Bitter Ordeal
Necroplasm
Yahenni's Expertise (cast and then ramp or extirpate or something)
Consume the Meek (anti lands, anti elves, anti regen)
Nature's Claim (anti artifact/enchantment for 1 mana allowing removal for 5)
Deathmark (kill for 1)
Dark Betrayal (kill for 1)
Doom Blade (kill for 2)
Krosan Grip (niche)
Cranial Extraction #2
Elixir of Immortality #2