Spells are events. Can I play a monster during opponent turn? (although the monster is destroyed at the end of the turn)
When Opener is in play, even monsters in your hand are spells. Note that "Spell" is a subtype, not a card type though. A subtype is just a way for cards to identify each other, but have no other rules meaning. Since monsters, dispite they gain a subtype common on event cards, still follow the rules of character cards, you can play them only during your own operations phase, as it states in the rules.
Similarly, when you give a character the "Location" subtype, commenly found on support cards, it doesn't make them a support card. They'll be quite safe from Burrowing Beneath and the likes. The latter means that:
-- Shub-Niggurath --
Type : Character
Cost : 6
Skill : 3
Icons : TTCC
Subtype : Monster.
Game Text: Action: sacrifice Cyclopean Dhole to destroy all Location cards. Action: exhaust and pay 3 to choose and destroy a Location card.
Collector's Info: AE R183
...can destroy a "location" character, but...
-- Agency --
Torch the Joint!
- Steadfast [AGENCY][AGENCY] -
Type : Event
Cost : 3
Game Text: Play during your operations phase. Action: choose and destroy a non-[Agency] resource or a Location support card.
Collector's Info: ASM F2
..can't because it specifically mentions support cards.
Also note that, besides the list of cards I mentioned a few posts back there are more cards that interact with cards that have the "spell" subtype. They do mention Event cards though, so unless the specific card you're trying to use has both the Monster subtype, and the Event card type, they can't be used in combination with Opener.
Card Type is written in the left lower corner of the card. Subtypes you'll find in the textbox. They are different, independant things that don't nessesary correlate all the time, despite trends you'll find among the cards.