A Taste of Power 
Sorcery
[X = 1+] Search your library for a card, put that card into your graveyard, then shuffle.
[X = 3+]: Search your library for a card and exile it face down, then shuffle. Put that card into your hand at the beginning of your next end step.
[X = 5+]: Search your library for a card, put that card into your hand, then shuffle.
Decided to get a bit creative with the templating.
(Also, hi guys. It's been a couple of years - formerly ThePianoPlayer on the old forums)
Power Level Discussion
- at two mana, it is entomb at sorcery speed. Obviously subpar, but any deck happy to play entomb would probably play a worse second copy that has other upside
- at four mana, it is entomb + delayed DT. Assuming that the entomb is relevant, is basically a delayed double tutor. Otherwise, is a Diabolic Tutor, which is also below par
- at six mana, it is entomb + delayed DT + DT. Assuming again that the entomb is relevant, it is a triple tutor. It might be too strong for only six mana?
Overall, I think the card may be a little pushed as is, but is hard to tweak values given the restriction of the challenge.
[Edit 1] Reworded second ability for clarity. Added Power Level Discussion
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: Switch Voidcaller’s power and toughness until end of turn.
"When in doubt, do a common."