Check out "The MOAT Mini Pack of Marching Bands" here: https://www.ephesusscroll.com/about/interest4.html. US$5 gets you 7 Marching Bands which, hard enough on their own, now contain metas too. And once again there's a mega-meta!
Activity involving the imagination and dice (abbr.)
13A
Start ___ (again)
14A
Important number in the book of Revelation (think seals, trumpets, and bowls)
15A
Pokemon that eats iron to build up the steel armour that protects its body (and whose name seems to be formed from smooshing "armour" and "iron" together)
17A
"Where ___ go wrong?"
18A
First month in Spain
19A
Region
20A
Surrounded by
22A
Person definitely not involved in 36 across because they would have stayed with family (see 55 across)
24A
Feed trough located in the place where 36 across occurred
26A
Be in Germany
27A
Doctor of Education (abbr.)
28A
Anglo-Saxon labourers
30A
Like van Gogh's night painting
32A
Amy Winehouse's most successful single
35A
Administrative division (abbr.)
36A
Name for the event that took place the very first Christmas
40A
"I've worked out the meta!"
41A
"___ little silhouetto of a man" (Queen lyric)
42A
31 down units
45A
Started
48A
Mensa stats
49A
Channel with many out-of-this-world shows
52A
Person involved in 36 across
55A
Place that was full of relatives, so 36 across took place where the animals were kept at night
58A
Cubic meter
59A
1003, on a cornerstone perhaps
60A
Actor ___ Elba
62A
Anagram of a term of endearment which is itself found in the word "endearment"
63A
River through Florence
64A
"I disagree, homie"
65A
"The Bookseller of Kabul" author ___ Seierstad
66A
Dusk, but in poetry
67A
Short wavelength radiation
68A
People involved in 36 across
Verticali
1D
Start of the palindrome that ends with "I'm Adam"
2D
Inner self, according to Jung
3D
Decorated again
4D
Bombing ships in the Star Wars universe
5D
Enzyme suffix
6D
River through La Paz
7D
Bakery fixtures
8D
Author whose works would be suitable for showing on 49 across, Jules ___
9D
Japanese mushrooms
10D
Destroy completely
11D
Stuff belonging to someone
12D
Evaporated, as a salt lake
16D
Geeklike
21D
Science Fiction, for example
23D
Treebeard, for example
25D
South Welsh term for a drainage ditch
29D
R&B group, known for the song "If I Ever Fall in Love"
31D
Grouping of 42 across
33D
@@@
34D
Singer Justin, for short
36D
River through Paris
37D
Chinese dynasty
38D
Music video programmer (but shortened in part)
39D
Othello's answer to, "Who's wife is Emilia?"
40D
Obtain
42D
Greek letter used in integrals
43D
Superlative suffix
44D
Fluid-filled cavity within the spinal cord
46D
Adjective for a boiling kettle
47D
Podcast "Conan O'Brien ___ Friend"
50D
Big name in travel guides
51D
___ Linda, California (and one letter changed from a famous Greek)
53D
Aussie slang for a car crash
54D
What Luther supposedly said at the Diet of Worms, "___ stand, I can do no other"
56D
Jerusalem mount (var.)
57D
"He brought me up also out of an horrible pit, out of the ___ clay" (Ps. 40:2, KJV)