Your cat likes me more
In brightest day / In blackest night / No evil shall escape my sight / Let those who worship evil's might / Beware my power--Green Lantern's light!
The aim of this variant is to allow you use events and energy shards without actually shuffling them into the portal deck. This helps keep the already large portal deck from ballooning in size, and also evens out the distribution of these random elements.
Basically, the idea is to roll a die whenever you put a card into the center row.
There should be 5-10 event cards per hundred cards in your portal deck. There should be 30 energy shards per hundred cards in your portal deck.
You'll want to set aside all the energy shards into a face-up stack, and shuffle all the events to form an event deck.
We can roll a d10, then, whenever we need to replace a card in the center row:
1-6: Add a card from the portal deck to the center row.
7: Turn over a new event from the event deck, then roll again.
8-10: Add an energy shard to the center row, then roll again.
This is already a fairly fiddle concept, and the die forcing a re-roll 40% of the time could really draw out the game. So instead, I think it might be better to abstract one layer further. Exploding only really matters in the case of energy shards. There's a 3/10 chance of getting at least one, a 9/100 chance of getting at least 2, and a 27/1000 chance of getting at least 3.
It's not perfect, but if we use a d20, we can have:
1-12: Add a card from the portal deck to the center row.
13-14: Turn over a new event from the event deck, then add a card to the center row from the portal deck.
15-17: Add one energy shard to the center row, then add a card from the portal deck on top of it.
18-19: Add two energy shards to the center row, then add a card from the portal deck on top of them.
20: Add three energy shards to the center row, then add a card from the portal deck on top of them.
One thing you lose with this style is there's no chance of drawing both an event and an energy shard... But I think that's acceptable.
This kind of reminds me of Magic's Planechase variant, only with a much higher chance of something changing each turn. Seems cool.