My general approach would be to make chickens, but let's say you're somehow at a point where you have the 13-15k energy you're going to want to do the fusion (and your other resources line up)

That is when I would be fine stockpiling. Otherwise you're limiting your account growth without enough payoff, though I think this specific fusion (and a few of the recent ones like Helicath) are worth momentarily holding back account growth for long term gains. 

I try to keep my current energy under the cap so I'm making free energy as much as possible.  Every 2 or 3 days you get a refill from the free daily packs (small, appreciation, etc).  These can be stockpiled in inbox.  I have 30+ atm.  The daily is spent building up food/ silver etc to make sure you have enough to complete the events.

the last event I went for was tomb dreng.  I had plenty of food/silver and didn't have to use a single refil from the inbox, other than a 999 energy they gave us as a reward that had a 6 day expiration.  Other than that the daily energy was all I needed for events.

my suggestion is to stockpile food and silver, shards and gems.  And use all the daily as you can.

I never even get close to that much energy save unfortunately. I usually get around 2k saved up, as I'm generally playing in most larger events or usually preparing for them. 

I guess another "problem" is that I have the CVC tournament energy in my inbox, but it runs out in like 3 days I think (450 energy) and tomorrow I'm getting 500 energy for Daily Login Day 85. That means I would have to burn through that 950 energy, or I can save it right 

The clear answer here is - if you're active enough, there's absolutely no reason to not be spending all of your energy every day. As you noted, by not doing so, you are losing a significant amount of free energy.

However, if you're only able to log in once or twice a day, the free energy you get isn't going to add up to much, and the value you'd gain by stockpiling actual energy to save for fusions will likely outweigh the benefit of the modest amount of extra food you'll get.

I guess there's 1 other factor for me Kram, I noted above that tomorrow I get my 85 day login which is 500 energy, as well as the CVC energy that is sitting in my inbox is set to expire soon. That would technically mean I need to burn through that 950 energy before I start up the Fusion event. 

It's not really enough of a factor. The fusion will start on September 9th - so if you stockpile energy instead of spending it, you're losing out on five days worth of free energy. Assuming you're active, you'll wake up in the morning with full energy, and then get roughly 16 hours worth of free energy (assuming eight hours of sleep), which translates into about 320 energy. Over six days, that's almost 2000 energy you're losing by stockpiling.

Makes sense. What's the most efficient thing for me to do to prepare for the fusion? Creating fat chickens? 

For the fusion specifically? Farm chickens and horde silver.

For other times, masteries and chickens.

Yes.  fat chickens in tavern, skinny chickens in mailbox! Make sure to let any tournament/event energy between now and then go to mailbox as well.

Just to elaborate on what Trips means - any rewards from events, tournaments, and CVC will automatically go to your mailbox if unclaimed. They'll then have ~6 days to use before they expire in the mailbox.

To note - rewards from daily/weekly/advanced quests do NOT go to mailbox if unclaimed, and rewards from daily login, as well as from Doom Tower rooms, are automatically claimed (and thus will never go to mailbox or expire).

Rewards from Faction Wars and Campaign never expire, and can be claimed at any point, although you cannot advance to the next set of rewards until you claim all the previous rewards (I believe). Rewards from missions never expire, although you cannot advance to the next mission without claiming them.

One thing I haven't personally tested is what happens to unclaimed rewards from arena (both classic and tag), Clan Boss, and Hydra. My guess though is that they'd expire and wouldn't go to mailbox.

Yeah, in this case I'm going to go with the crowd here and say we need to be using that energy for fusion prep and account growth. :)

Missing out on that free energy every day is quite rough, even in this specific case. 

For clan boss it won't expire but will disappear when you leave the clan

I can add that Classic Arena chests accumulate.  My clanmate never collected for a while, had over 40 Gold 4 chests waiting to  be 

Good way to "cheat" the inventory/mailbox system for hoarders? Lol