Set the Power Limits challenge to "No Temporary Powers" before starting a level 50 Flashback from the Pillar of Ice and Flame. Then, complete the Flashback. Level 50+ (Incarnate / Evil Incarnate) Flashbacks don't count.

Usable powers

Certain temporary and day job powers

Jet packs, Alignment Powers

Temporary powers required for mission completion

Mark and Recall

Certain fast travel powers

Long Range Teleporter, Ouroboros Portal

Disabled powers

Most other temporary and day job powers

All other fast travel powers

Base Transporter, Supergroup Portal, Mission Transporter, Team Transporter, Assemble the Team

Prestige attacks