This has been widely discussed and for a reason. There’s a couple of very good tools. This is my take.

One way to design a deck is to go back from how you want the turn you win to go. In this case, we want to cast [scryfall]Aspect of Hydra[/scryfall] and push enough damage through that way. So, we begin with a set of those. Then, we need have enough pips to get the damage we want. So, our curve should be very good.

One-Drops

There’s nine creatures with the mana cost of G in the current standard. Some of them are just too slow ([scryfall]Renonwed Weaver[/scryfall] or awkward [scryfall]Kin-Tree Warden[/scryfall] or are closely linked to other color ([scryfall]Warden of the First Tree[/scryfall], [scryfall]Sunblade Elf[/scryfall]), which leaves us with just five:

[scryfall]Elvish Mystic[/scryfall] is in, no question. I didn’t like it when I was playing a similar deck last year, but now I feel I need them to be fast enough. Second turn [scryfall]Boon Satyr[/scryfall] or [scryfall]Deathmist Raptor[/scryfall] is very good.

The utility of [scryfall]Hero of Leina Tower[/scryfall] is largely dependent on how many tricks we play. We do have the four [scryfall]Aspect of Hydra[/scryfall]s, but are we playing [scryfall]Gather Gourage[/scryfall]? [scryfall]Epic Confrontation[/scryfall]? [scryfall]Titanic Growth[/scryfall]? Maybe even [scryfall]Ranger’s Guile[/scryfall] and [scryfall]Hunt the Hunter[/care] after sideboarding? I’d say we put her in. At least at this point.

[scryfall]Charging Badger[/scryfall] does have the nice benefit of having tremple and it might come in handy.

[scryfall]Servant of the Scale[/scryfall] helps with [scryfall]Avatar of the Resolute[/scryfall] and also leaves a nice bonus behind when it dies. Actually, I don’t see you being able to use the bonus very often, but you never know.

[scryfall]Sedge Scorpion[/scryfall] feels like a bit too defensive. If we were able to somehow give it trample, it would be nice, but I don’t see that happening.

Two-Drops

There’s 27 of these, so I’m not going to go through them card by card, only the more interesting ones:

Avatar is in. More power then casting cost and two pips of devotion, plus trample. Yes, that is in.

[scryfall]Den Protector[/scryfall] is also a nice card. The pseudo evasion can be really good at times, because you can grow her with Aspect.

[scryfall]Heir of the Wilds[/scryfall] is a bit problematic. If we have enough power 4, it will work out nicely, but that would require testing.

[scryfall]Scaleguard Sentinels[/scryfall] is probably not stong enough. We won’t have any dragons in the deck, so he will never get the bonus, so he’s out.

[scryfall]Swordwise Centaur[/scryfall] is strictly worse than the Avatar, but might still make the cut, because of its two pips and three power.

[scryfall]Temur Charger[/scryfall]… hard to say. It would be good at times, but how often? Its easy enough to turn face up, at least and the ability is definitely strong.

Three-Drops

There’s 29, but only four relevant ones.

This is a difficult one. I sort of like them all.

The flash on [scryfall]Boon Satyr[/scryfall] is extremely good. I’ve won so many games with it.

[scryfall]Deathmist Raptor[/scryfall] gives us a chance to go long. Also, if we play [scryfall]Den Protector[/scryfall] there’s a good chance we can return it to the table.

[scryfall]Reverent Hunter[/scryfall] gives us another way to benefit from the devotion we should have plenty of. It can be very big, but might sometimes strike out.

[scryfall]Yasova Dragonclaw[/scryfall] has trample and does trigger ferocious.

Four-Drops

IF we go this high, I know exactly what we want:

So, with all that in mind, this might be a good starting point:

[deck]
[creatures]
4 Elvish Mystic
4 Hero of Leina Tower
2 Servant of the Scale
4 Avatar of the Resolute
4 Den Protector
2 Swordwise Centaur
4 Deathmist Raptor
4 Boon Satyr
2 Reverent Hunter
2 Surrak, the Hunt Caller
[/creatures]
[spells]
4 Aspect of Hydra
3 Gather Courage
[/spells]
[lands]
21 Forest
[/lands]
[/deck]

Note: There are other tricks you might consider. [scryfall]Life’s Legacy[/scryfall] might be very good. You can pump your creature with [scryfall]Boon Satyr[/scryfall] or [scryfall]Aspect of Hydra[/scryfall] and then cash him in after combat with this and draw a bunch of cards. There must be other good deck out there, but this is something you might want to try. Sadly, it doesn’t target (which would be nice with [scryfall]Hero of Leina Tower[/scryfall]).