Sweet,
Mesmerizing Benthid. Cool card, but there are probably better things to
polymorph into, sadly.
If you want my general thoughts, then here they are:
Use less "small" value creatures and play token creation cards instead, while reserving those sweet
polymorph slots in your deck for big creatures only, or creatures that create more tokens, like
Talrand, Sky Summoner and
Murmuring Mystic. You have some notable creatures of that category, namely
Nadir Kraken and
Chasm Skulker. If you want to go the
polymorph route, focus hard on that. Your opponents should
dread you untapping with Jalira.
Here are some resources. Heavy control is probably necessary, because good players won't let you untap with a card that says "2U, T, sacrifice a creature: Put your choice of eldritch horror onto the battlefield."
Regarding untapping, you already use
Magewright's Stone, why not add
Thousand-Year Elixir, too? You could cut
Helm of the Host for that, since it's just a lot of mana spent for nothing when your plan is already working.