Rule 355.9
A target is a valid choice if it meets all of the following requirements:
- 355.9.a It is a permanent or rune on the board, a spell or ability on the chain, a player or zone, or specified explicitly or…
- 355.9.b It meets all targeting restrictions. e.g., A unit is a valid target for a spell that refers to a “unit at a…
- 355.9.c It is not the spell or ability itself. e.g., A spell that says “Counter a spell” cannot target itself. e.g., An…