Quote Originally Posted by Aijalom View Post
An first hand Sp+ Hermits have 80% chance. If first hand is an SP without oracle or Dread return, your next mulligan hand is an 70% 8 hermit chance...i dont think mulligan switch SP, but SP reinforce mulligan, not?
London Mulligan has about the same chance to find Hermit as using SP.
The main difference is SP lets you keep a 7th card, but you have to exile the first 7 (hope you didn't have an essential combo piece there).

Serum Powder Pros:
-Slightly higher chance of seeing Hermit, because you exiled 7 non-Hermit cards (70.6% on 2nd hand vs 65.4% from London mull)
-Keep 7 cards in new hand
-Improves next mulligan/SP if you have to ship that hand too

Cons:
-Risk of exiling combo pieces (can't use with DR or Thassa in hand, risky with Narc or Bridge)
-If you don't need it to find Hermit, it's a dead slot that doesn't even pitch to Mox or Unmask/Force (i.e. every time you draw it and don't need it, you effectively mulliganned -1 card)

Is that worth it overall? It might still help. It's just less of an edge than it used to be pre-London.

It only boosts the 2nd hand by about 5%, and keeping the best 6 of 7 is still enough to go off. SP would show more of a difference after multiple mulligans/SPs, because of both the cards you exile and getting to keep a bigger hand with more resources.