Some mechanical themes and elements of Theros include:
Enchantments - mostly creatures that are also enchantments, but also some of the regular kinds you're used to from other planes. Ties into ... Bestow - some enchantment creatures can be cast as an Aura, in which case they give the enchanted creature benefits related to their own power and toughness and abilities. If a creature cast this way would be unattached from the enchanted creature (like if it dies), it stays in play and becomes a regular creature. Bestow plays well with...
Heroic - a keyword that rewards you for targeting your creature with your own spells.
Constellation - the obligatory "why the heck is this even a keyword/ability word?" moment that we tend to get about once a block. Cards with Constellation have a significant effect that triggers whenever an enchantment comes into play under your control.
|Settings of Magic: The Gathering|
|Pre-revisionist:|| First Magic Sets - First Urza Block - Arabian Nights |
Legends - Homelands - Ice Age - Mirage
|Weatherlight Saga:|| Portal Starter Sets - Second Urza Block |
Tempest Block - Masques Block - Invasion Block
|Post-Weatherlight:||Otaria Block - Mirrodin - Kamigawa - Ravnica - Time Spiral|
|After the Mending:|| Lorwyn - Alara - Zendikar - New Phyrexia |
Innistrad - Return to Ravnica - Theros - Tarkir
|Two-Block Paradigm:||Kaladesh - Amonkhet - Ixalan|
|Never in a standard set:||Fiora (Where the Conspiracy sets take place)|