Hey,
some suggestions:
1. Clean up the land base. Muldrotha already isn't fast, because of her high cmc. The amount of tapped lands you play even delay you futher.
2. add some more mana ramp. With step 1 done, you'll end up with more basics (or raising the budget). Add some more ramp then, for colorfixing and acceleration.
3. don't be greedy. Cards like
Mirror-Mad Phantasm are a big
gamble. They can give you a big advantage if used right, but a big selfmill followed by an opponents graveyard hate could break your neck. I prefere cards like
Monastery Siege or
Sultai Ascendancy here. They are slower but gives you more control over which and how many cards go into your graveyard.
I've got a muldrotha deck myself, buildrestriction was 100 permanents (so that I can get
everything back. It is build on a higher budget, but maybe you'll find some cards that fit into your deck.
https://deckstats.net/decks/112190/1051092-muldrotha-the-gravetide-perman