I've been working on some openers for the Beastmaster. I understand that there are spells like mana siphon, and drain mana - however I feel like that shouldn't stop you from having an opening plan.
My preferred method of play is to be a bit conservative and then attack with a few mid-large creatures buffed with enchants. However, I can't be greedy if my opponent is being aggressive so I like to give my opponent the initiative to get a sense of what they're up to and adjust accordingly. If I'm playing against a warlock who throws down a forward forge, or a beastmaster who puts on a ring of beasts and throws down a creature turn one, I know it's fightin' time and switch into my aggressive openers.
Here is what I have:
Format is my mana, hyphen, mana on my lair.
Slow - My default opener. I'll play this way if my opponent appears to be playing the long game.
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19-00 Turn 01
04-00 Lair
00-00 Harmonize (on lair)
09-03 Turn 02
04-03 Mana Flower
02-03 Nullify
12-06 Turn 03
06-00 Timber Wolf (Pet)
01-00 Mana Flower
12-03 Turn 04
09-00 Thunderrift Falcon
07-00 Tooth & Nail
00-00 Staff of Beasts
Slow into Aggro - If my opponent appeared to be playing a long game, then turned on the heat quickly
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19-00 Turn 01
04-00 Lair
00-00 Harmonize (on lair)
09-03 Turn 02
04-03 Mana Flower
02-03 Nullify (Not vs Beastmaster)
12-06 Turn 03
06-00 Timber Wolf (Pet)
04-00 Ring of Beasts
00-00 Bitterwood Fox
10-03 Turn 04
08-00 Bitterwood Fox
04-00 Bitterwood Fox
02-00 Enchantment
12-03 Turn 05
00-00 Redclaw
Aggro - If my opponent goes crazy aggressive and I need to keep up.
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19-00 Turn 01
17-00 Ring of Beasts
13-00 Bitterwood Fox
22-00 Turn 02
07-00 Redclaw
03-00 Rouse the Beast (if in range)
12-00 Turn 03
01-00 Timber Wolf (Pet)
01-00 None
10-00 Turn 04
06-00 Bitterwood Fox (or heal)
02-00 Bitterwood Fox
11-00 Turn 05
04-00 Tooth & Nail
02-00 Enchantment