8 Jun 2016
Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keywords are activated abilities and will have colons in their reminder text.
14 Mar 2017
If the enchanted creature's power isn't 4 or greater when the end step begins, the last ability won't trigger at all.
14 Mar 2017
Arachnus Web's triggered ability checks at the beginning of each end step, not just yours.
14 Mar 2017
If Arachnus Web's last ability triggers, but the enchanted creature's power is reduced to 3 or less before the ability resolves, the ability will have no effect. Arachnus Web won't be destroyed.
14 Mar 2017
Triggered abilities (starting with "when," "whenever," or "at") are unaffected.
14 Mar 2017
If Arachnus Web enters the battlefield attached to an attacking or blocking creature (due to Arachnus Spinner's ability, for example), that creature will continue to attack or block.